<?xml version="1.0" encoding="US-ASCII"?>
<!-- RR Donnelley Xcelerate Taxonomy Calculation Linkbase, based on XBRL 2.1  http://www.rrdonnelley.com/ -->
<!-- Version: 6.22.4 -->
<!-- Round: 8 -->
<!-- Creation date: 2015-08-10T15:37:31Z -->
<!-- Copyright (c) 2005-2013 R.R. Donnelley & Sons Company All Rights Reserved. -->
<linkbase xmlns="http://www.xbrl.org/2003/linkbase"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DocumentandEntityInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DocumentandEntityInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_StatementOfFinancialPositionClassified" roleURI="http://serestherapeutics.com/taxonomy/role/StatementOfFinancialPositionClassified"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_StatementOfFinancialPositionClassifiedParen" roleURI="http://serestherapeutics.com/taxonomy/role/StatementOfFinancialPositionClassifiedParenthetical"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_StatementOfIncome" roleURI="http://serestherapeutics.com/taxonomy/role/StatementOfIncome"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_StatementOfIncomeParen" roleURI="http://serestherapeutics.com/taxonomy/role/StatementOfIncomeParenthetical"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_StatementOfShareholdersEquityAndOtherComprehensiveIncome" roleURI="http://serestherapeutics.com/taxonomy/role/StatementOfShareholdersEquityAndOtherComprehensiveIncome"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_StatementOfCashFlowsIndirect" roleURI="http://serestherapeutics.com/taxonomy/role/StatementOfCashFlowsIndirect"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureNatureOfTheBusinessAndBasisOfPresentationAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureNatureOfTheBusinessAndBasisOfPresentationAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureSummaryOfSignificantAccountingPoliciesSummaryOfAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasis" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesSummaryOfAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasis"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureSummaryOfSignificantAccountingPoliciesSummaryOfPotentialCommonSharesExcludedFromCalculationOfDilutedNetLossPerShare" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesSummaryOfPotentialCommonSharesExcludedFromCalculationOfDilutedNetLossPerShare"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureInvestmentsScheduleOfFairValueOfAvailableforSaleInvestmentsByTypeOfSecurity" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureInvestmentsScheduleOfFairValueOfAvailableforSaleInvestmentsByTypeOfSecurity"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureInvestmentsAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureInvestmentsAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosurePropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNet" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosurePropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNet"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosurePropertyAndEquipmentNetAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosurePropertyAndEquipmentNetAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureAccruedExpensesAndOtherCurrentLiabilitiesSummaryOfAccruedExpensesAndOtherCurrentLiabilities" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesSummaryOfAccruedExpensesAndOtherCurrentLiabilities"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureNotesPayableAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureNotesPayableAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosurePreferredStockWarrantLiabilityAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosurePreferredStockWarrantLiabilityAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosurePreferredStockWarrantLiabilitySummaryOfAssumptionsAndInputsUsedInDeterminingFairValueOfPreferredStockWarrantLiabilityValuedUsingBlackScholesOptionPricingModel" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosurePreferredStockWarrantLiabilitySummaryOfAssumptionsAndInputsUsedInDeterminingFairValueOfPreferredStockWarrantLiabilityValuedUsingBlackScholesOptionPricingModel"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosurePreferredStockWarrantLiabilitySummaryOfRollforwardOfFairValueOfPreferredStockWarrantLiability" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosurePreferredStockWarrantLiabilitySummaryOfRollforwardOfFairValueOfPreferredStockWarrantLiability"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureConvertiblePreferredStockAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureConvertiblePreferredStockAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquityCommonStockAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquityCommonStockAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquityCommonStockWarrantAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquityCommonStockWarrantAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquity2012StockIncentivePlanAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquity2012StockIncentivePlanAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquity2015IncentiveAwardPlanAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquity2015IncentiveAwardPlanAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquity2015EmployeeStockPurchasePlanAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquity2015EmployeeStockPurchasePlanAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquitySummaryOfStockOptionActivity" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquitySummaryOfStockOptionActivity"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquityStockOptionsAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquityStockOptionsAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquitySummaryOfRestrictedStockActivity" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquitySummaryOfRestrictedStockActivity"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureStockholdersEquitySummaryOfStockBasedCompensationExpense" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquitySummaryOfStockBasedCompensationExpense"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureIncomeTaxesAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureIncomeTaxesAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureCommitmentsAndContingenciesAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#DisclosureRelatedPartyTransactionsAdditionalInformation" roleURI="http://serestherapeutics.com/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformation"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsBusinessDescriptionAndBasisOfPresentationTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsBusinessDescriptionAndBasisOfPresentationTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockPolicies" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockPolicies"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockTables" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockTables"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsInvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsInvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsInvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlockTables" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsInvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlockTables"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlockTables" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlockTables"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlockTables" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlockTables"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsDebtDisclosureTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsDebtDisclosureTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsPreferredStockWarrantsLiabilityDisclosureTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPreferredStockWarrantsLiabilityDisclosureTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsPreferredStockWarrantsLiabilityDisclosureTextBlockTables" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPreferredStockWarrantsLiabilityDisclosureTextBlockTables"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsPreferredStockTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPreferredStockTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsShareholdersEquityAndShareBasedPaymentsTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsShareholdersEquityAndShareBasedPaymentsTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsShareholdersEquityAndShareBasedPaymentsTextBlockTables" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsShareholdersEquityAndShareBasedPaymentsTextBlockTables"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsIncomeTaxDisclosureTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsCommitmentsAndContingenciesDisclosureTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsCommitmentsAndContingenciesDisclosureTextBlock"/>
  <roleRef xlink:type="simple" xlink:href="mcrb-20150630.xsd#Role_NotesToFinancialStatementsRelatedPartyTransactionsDisclosureTextBlock" roleURI="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsRelatedPartyTransactionsDisclosureTextBlock"/>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DocumentandEntityInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/StatementOfFinancialPositionClassified">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:label="us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdditionalPaidInCapitalCommonStock" xlink:label="us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredFinanceCostsNoncurrentNet" xlink:label="us-gaap_DeferredFinanceCostsNoncurrentNet"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredOfferingCosts" xlink:label="us-gaap_DeferredOfferingCosts"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LongTermNotesPayable" xlink:label="us-gaap_LongTermNotesPayable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NotesPayableCurrent" xlink:label="us-gaap_NotesPayableCurrent"/>
    <loc xlink:type="locator" xlink:href="mcrb-20150630.xsd#mcrb_PreferredStockWarrantLiability" xlink:label="mcrb_PreferredStockWarrantLiability"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount" xlink:label="us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsNoncurrent" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsNoncurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="us-gaap_ShortTermInvestments"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Assets" xlink:to="us-gaap_AssetsCurrent" order="1.0400" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Assets" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" order="1.0500" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Assets" xlink:to="us-gaap_RestrictedCashAndCashEquivalentsNoncurrent" order="1.0600" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Assets" xlink:to="us-gaap_DeferredOfferingCosts" order="1.0700" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Assets" xlink:to="us-gaap_DeferredFinanceCostsNoncurrentNet" order="1.0800" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" order="1.0100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_ShortTermInvestments" order="1.0200" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" order="1.0300" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_LiabilitiesCurrent" order="1.1200" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_LongTermNotesPayable" order="1.1300" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_Liabilities" xlink:to="mcrb_PreferredStockWarrantLiability" order="1.1400" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_Liabilities" order="1.1500" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_StockholdersEquity" order="1.2000" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount" order="1.2100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_AccountsPayableCurrent" order="1.0900" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesAndOtherLiabilities" order="1.1000" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_NotesPayableCurrent" order="1.1100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_CommonStockValue" order="1.1600" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_AdditionalPaidInCapitalCommonStock" order="1.1700" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" order="1.1800" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" order="1.1900" weight="1.00" priority="2" use="optional"/>
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/StatementOfFinancialPositionClassifiedParenthetical">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/StatementOfIncome">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueOptionChangesInFairValueGainLoss1" xlink:label="us-gaap_FairValueOptionChangesInFairValueGainLoss1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="us-gaap_GeneralAndAdministrativeExpense"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="us-gaap_NonoperatingIncomeExpense"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="us-gaap_OperatingExpenses"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="us-gaap_ResearchAndDevelopmentExpense"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_ComprehensiveIncomeNetOfTax" xlink:to="us-gaap_NetIncomeLoss" order="1.0900" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_ComprehensiveIncomeNetOfTax" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTax" order="1.1100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss" order="1.0500" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NonoperatingIncomeExpense" order="1.0800" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NonoperatingIncomeExpense" xlink:to="us-gaap_InterestIncomeExpenseNet" order="1.0600" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NonoperatingIncomeExpense" xlink:to="us-gaap_FairValueOptionChangesInFairValueGainLoss1" order="1.0700" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_ResearchAndDevelopmentExpense" order="1.0200" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_GeneralAndAdministrativeExpense" order="1.0300" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_Revenues" order="1.0100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingExpenses" order="1.0400" weight="-1.00" priority="2" use="optional"/>
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/StatementOfIncomeParenthetical">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/StatementOfShareholdersEquityAndOtherComprehensiveIncome">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/StatementOfCashFlowsIndirect">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="us-gaap_DepreciationDepletionAndAmortization"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueOptionChangesInFairValueGainLoss1" xlink:label="us-gaap_FairValueOptionChangesInFairValueGainLoss1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInRestrictedCash" xlink:label="us-gaap_IncreaseDecreaseInRestrictedCash"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss"/>
    <loc xlink:type="locator" xlink:href="mcrb-20150630.xsd#mcrb_NoncashInterestExpense" xlink:label="mcrb_NoncashInterestExpense"/>
    <loc xlink:type="locator" xlink:href="mcrb-20150630.xsd#mcrb_PaymentOfLicenseFeesInCommonStockWarrant" xlink:label="mcrb_PaymentOfLicenseFeesInCommonStockWarrant"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PaymentsForRepurchaseOfInitialPublicOffering" xlink:label="us-gaap_PaymentsForRepurchaseOfInitialPublicOffering"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="us-gaap_PaymentsToAcquireInvestments"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <loc xlink:type="locator" xlink:href="mcrb-20150630.xsd#mcrb_ProceedsFromExerciseOfStockOptionsAndCommonStockWarrants" xlink:label="mcrb_ProceedsFromExerciseOfStockOptionsAndCommonStockWarrants"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" xlink:label="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ProceedsFromNotesPayable" xlink:label="us-gaap_ProceedsFromNotesPayable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments" xlink:label="us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RepaymentsOfNotesPayable" xlink:label="us-gaap_RepaymentsOfNotesPayable"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" order="1.1000" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" order="1.1500" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" order="1.2100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:to="us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" order="1.1600" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:to="us-gaap_ProceedsFromNotesPayable" order="1.1700" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:to="mcrb_ProceedsFromExerciseOfStockOptionsAndCommonStockWarrants" order="1.1800" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:to="us-gaap_RepaymentsOfNotesPayable" order="1.1900" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:to="us-gaap_PaymentsForRepurchaseOfInitialPublicOffering" order="1.2000" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" order="1.1100" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:to="us-gaap_PaymentsToAcquireInvestments" order="1.1200" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:to="us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments" order="1.1300" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:to="us-gaap_IncreaseDecreaseInRestrictedCash" order="1.1400" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_NetIncomeLoss" order="1.0100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_ShareBasedCompensation" order="1.0200" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_DepreciationDepletionAndAmortization" order="1.0300" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_FairValueOptionChangesInFairValueGainLoss1" order="1.0400" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="mcrb_PaymentOfLicenseFeesInCommonStockWarrant" order="1.0500" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="mcrb_NoncashInterestExpense" order="1.0600" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" order="1.0700" weight="-1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayable" order="1.0800" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" order="1.0900" weight="1.00" priority="2" use="optional"/>
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureNatureOfTheBusinessAndBasisOfPresentationAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesSummaryOfAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasis">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="us-gaap_AssetsFairValueDisclosure"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="us-gaap_InvestmentsFairValueDisclosure"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AssetsFairValueDisclosure" xlink:to="us-gaap_CashAndCashEquivalentsFairValueDisclosure" order="1.0100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AssetsFairValueDisclosure" xlink:to="us-gaap_InvestmentsFairValueDisclosure" order="1.0200" weight="1.00" priority="2" use="optional"/>
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesSummaryOfPotentialCommonSharesExcludedFromCalculationOfDilutedNetLossPerShare">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureInvestmentsScheduleOfFairValueOfAvailableforSaleInvestmentsByTypeOfSecurity">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureInvestmentsAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosurePropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNet">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="us-gaap_PropertyPlantAndEquipmentGross"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_PropertyPlantAndEquipmentGross" order="1.0200" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" order="1.0300" weight="-1.00" priority="2" use="optional"/>
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosurePropertyAndEquipmentNetAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesSummaryOfAccruedExpensesAndOtherCurrentLiabilities">
    <loc xlink:type="locator" xlink:href="mcrb-20150630.xsd#mcrb_AccruedDevelopmentAndManufacturingCostsCurrent" xlink:label="mcrb_AccruedDevelopmentAndManufacturingCostsCurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:label="us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccruedProfessionalFeesCurrent" xlink:label="us-gaap_AccruedProfessionalFeesCurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:to="mcrb_AccruedDevelopmentAndManufacturingCostsCurrent" order="1.0100" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:to="us-gaap_EmployeeRelatedLiabilitiesCurrent" order="1.0200" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:to="us-gaap_AccruedProfessionalFeesCurrent" order="1.0300" weight="1.00" priority="2" use="optional"/>
    <calculationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent" order="1.0400" weight="1.00" priority="2" use="optional"/>
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureNotesPayableAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosurePreferredStockWarrantLiabilityAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosurePreferredStockWarrantLiabilitySummaryOfAssumptionsAndInputsUsedInDeterminingFairValueOfPreferredStockWarrantLiabilityValuedUsingBlackScholesOptionPricingModel">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosurePreferredStockWarrantLiabilitySummaryOfRollforwardOfFairValueOfPreferredStockWarrantLiability">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureConvertiblePreferredStockAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquityCommonStockAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquityCommonStockWarrantAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquity2012StockIncentivePlanAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquity2015IncentiveAwardPlanAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquity2015EmployeeStockPurchasePlanAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquitySummaryOfStockOptionActivity">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquityStockOptionsAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquitySummaryOfRestrictedStockActivity">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureStockholdersEquitySummaryOfStockBasedCompensationExpense">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureIncomeTaxesAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformation">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsBusinessDescriptionAndBasisOfPresentationTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockPolicies">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockTables">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsInvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsInvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlockTables">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlockTables">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsAccountsPayableAccruedLiabilitiesAndOtherLiabilitiesDisclosureCurrentTextBlockTables">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsDebtDisclosureTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPreferredStockWarrantsLiabilityDisclosureTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPreferredStockWarrantsLiabilityDisclosureTextBlockTables">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsPreferredStockTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsShareholdersEquityAndShareBasedPaymentsTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsShareholdersEquityAndShareBasedPaymentsTextBlockTables">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsCommitmentsAndContingenciesDisclosureTextBlock">
  </calculationLink>
  <calculationLink xlink:type="extended" xlink:role="http://serestherapeutics.com/taxonomy/role/NotesToFinancialStatementsRelatedPartyTransactionsDisclosureTextBlock">
  </calculationLink>
</linkbase>
