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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-11-12T09:05:19.1709201+00:00 -->
<!-- Version            : 5.0.1.513 -->
<!-- Package ID         : 2753518f2a3f4abda6ca47045a21386c -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="ngm_RemainingOperatingLeasePaymentsFromRelatedPartyToLessor" name="RemainingOperatingLeasePaymentsFromRelatedPartyToLessor" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_StockOptionFiscalTwentyEighteenPlanMember" name="StockOptionFiscalTwentyEighteenPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_NonEmployeesMember" name="NonEmployeesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_FourZeroOneKMatchingPlanMember" name="FourZeroOneKMatchingPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommonStockOptionsOutstandingMember" name="CommonStockOptionsOutstandingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommonStockOptionsAvailableForGrantMember" name="CommonStockOptionsAvailableForGrantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantsInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantsInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantExercisedInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantExercisedInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeituresInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeituresInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_TwoThousandEightAndTwoThousandEighteenPlanMember" name="TwoThousandEightAndTwoThousandEighteenPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_EmployeesAndDirectorsMember" name="EmployeesAndDirectorsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_OfferingPeriodForPurchaseUnderEmployeeStockPurchasePlan" name="OfferingPeriodForPurchaseUnderEmployeeStockPurchasePlan" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_NumberOfPurchasePeriods" name="NumberOfPurchasePeriods" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_DurationOfEachPurchasePeriod" name="DurationOfEachPurchasePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_CARESActOf2020AidNetOperatingLossCarryForwardPeriod" name="CARESActOf2020AidNetOperatingLossCarryForwardPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_CARESActOf2020AidNetOperatingLossesCarryforwardMaximumPercentageOfTaxableIncome" name="CARESActOf2020AidNetOperatingLossesCarryforwardMaximumPercentageOfTaxableIncome" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
