content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
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      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001507220</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <issuerCik>0001395937</issuerCik>
        <issuerName>Syndax Pharmaceuticals Inc</issuerName>
        <secFileNumber>001-37708</secFileNumber>
        <issuerAddress>
          <com:street1>35 GATEHOUSE DRIVE</com:street1>
          <com:street2>BUILDING D, FLOOR 3</com:street2>
          <com:city>WALTHAM</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02451</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>781-419-1400</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Metzger Michael A</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>Officer</relationshipToIssuer>
          <relationshipToIssuer>Director</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>Fidelity Brokerage Services LLC</name>
          <address>
            <com:street1>900 Salem Street</com:street1>
            <com:city>Smithfield</com:city>
            <com:stateOrCountry>RI</com:stateOrCountry>
            <com:zipCode>02917</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>13288</noOfUnitsSold>
        <aggregateMarketValue>206017.15</aggregateMarketValue>
        <noOfUnitsOutstanding>85357675</noOfUnitsOutstanding>
        <approxSaleDate>02/10/2025</approxSaleDate>
        <securitiesExchangeName>NASDAQ</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>02/07/2025</acquiredDate>
        <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>13288</amountOfSecuritiesAcquired>
        <paymentDate>02/07/2025</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <remarks>Sale includes an amount necessary to cover a tax obligation resulting from the settlement of a vested equity award distribution.</remarks>
      <noticeSignature>
        <noticeDate>02/10/2025</noticeDate>
        <signature>/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Michael A. Metzger</signature>
      </noticeSignature>
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text: 144
  0001507220
  XXXXXXXX
  LIVE
  0001395937
  Syndax Pharmaceuticals Inc
  001-37708
  35 GATEHOUSE DRIVE
  BUILDING D, FLOOR 3
  WALTHAM
  MA
  02451
  781-419-1400
  Metzger Michael A
  Officer
  Director
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  13288
  206017.15
  85357675
  02/10/2025
  NASDAQ
  Common
  02/07/2025
  Restricted Stock Vesting
  Issuer
  N
  13288
  02/07/2025
  Compensation
  Y
  Sale includes an amount necessary to cover a tax obligation resulting from the settlement of a vested equity award distribution.
  02/10/2025
  /s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Michael A. Metzger