-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 CWaTzDSw2eN6CrW6WtolZQ==

<SEC-DOCUMENT>0000898432-10-001033.txt : 20100805
<SEC-HEADER>0000898432-10-001033.hdr.sgml : 20100805
<ACCEPTANCE-DATETIME>20100805114415
ACCESSION NUMBER:		0000898432-10-001033
CONFORMED SUBMISSION TYPE:	D
PUBLIC DOCUMENT COUNT:		1
ITEM INFORMATION:		Rule 506
FILED AS OF DATE:		20100805
DATE AS OF CHANGE:		20100805
EFFECTIVENESS DATE:		20100805

FILER:

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Syndax Pharmaceuticals Inc
		CENTRAL INDEX KEY:			0001395937
		IRS NUMBER:				320162505
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		D
		SEC ACT:		1933 Act
		SEC FILE NUMBER:	021-145970
		FILM NUMBER:		10993334

	BUSINESS ADDRESS:	
		STREET 1:		460 TOTTEN POND ROAD
		STREET 2:		SUITE 650
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02451
		BUSINESS PHONE:		781-419-1400

	MAIL ADDRESS:	
		STREET 1:		460 TOTTEN POND ROAD
		STREET 2:		SUITE 650
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02451
</SEC-HEADER>
<DOCUMENT>
<TYPE>D
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<edgarSubmission>

    <schemaVersion>X0704</schemaVersion>

    <submissionType>D</submissionType>

    <testOrLive>LIVE</testOrLive>

    <primaryIssuer>
        <cik>0001395937</cik>
        <entityName>Syndax Pharmaceuticals Inc</entityName>
        <issuerAddress>
            <street1>460 TOTTEN POND ROAD</street1>
            <street2>SUITE 650</street2>
            <city>WALTHAM</city>
            <stateOrCountry>MA</stateOrCountry>
            <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
            <zipCode>02451</zipCode>
        </issuerAddress>
        <issuerPhoneNumber>781-419-1400</issuerPhoneNumber>
        <jurisdictionOfInc>DELAWARE</jurisdictionOfInc>
        <issuerPreviousNameList>
            <value>None</value>
        </issuerPreviousNameList>
        <edgarPreviousNameList>
            <value>None</value>
        </edgarPreviousNameList>
        <entityType>Corporation</entityType>
        <yearOfInc>
            <withinFiveYears>true</withinFiveYears>
            <value>2005</value>
        </yearOfInc>
    </primaryIssuer>

    <relatedPersonsList>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Joanna</firstName>
                <lastName>Horobin, M.D.</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>460 Totten Pond Road</street1>
                <street2>Suite 650</street2>
                <city>Waltham</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02451</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification>President and Chief Executive Officer</relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Robert</firstName>
                <lastName>Goodenow, PhD</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>460 Totten Pond Road</street1>
                <street2>Suite 650</street2>
                <city>Waltham</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02451</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Kim</firstName>
                <lastName>Kamdar, PhD</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>460 Totten Pond Road</street1>
                <street2>Suite 650</street2>
                <city>Waltham</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02451</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Rosina</firstName>
                <lastName>Maar Pavia, M.D.</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>460 Totten Pond Road</street1>
                <street2>Suite 650</street2>
                <city>Waltham</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02451</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Steven</firstName>
                <lastName>St. Peter, M.D.</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>460 Totten Pond Road</street1>
                <street2>Suite 650</street2>
                <city>Waltham</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02451</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Dennis</firstName>
                <lastName>Podlesak</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>460 Totten Pond Road</street1>
                <street2>Suite 650</street2>
                <city>Waltham</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02451</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
        </relatedPersonInfo>
    </relatedPersonsList>

    <offeringData>
        <industryGroup>
            <industryGroupType>Pharmaceuticals</industryGroupType>
        </industryGroup>
        <issuerSize>
            <revenueRange>Decline to Disclose</revenueRange>
        </issuerSize>
        <federalExemptionsExclusions>
            <item>06</item>
        </federalExemptionsExclusions>
        <typeOfFiling>
            <newOrAmendment>
                <isAmendment>false</isAmendment>
            </newOrAmendment>
            <dateOfFirstSale>
                <value>2010-08-03</value>
            </dateOfFirstSale>
        </typeOfFiling>
        <durationOfOffering>
            <moreThanOneYear>false</moreThanOneYear>
        </durationOfOffering>
        <typesOfSecuritiesOffered>
            <isDebtType>true</isDebtType>
            <isOptionToAcquireType>true</isOptionToAcquireType>
        </typesOfSecuritiesOffered>
        <businessCombinationTransaction>
            <isBusinessCombinationTransaction>false</isBusinessCombinationTransaction>
        </businessCombinationTransaction>
        <minimumInvestmentAccepted>0</minimumInvestmentAccepted>
        <salesCompensationList></salesCompensationList>
        <offeringSalesAmounts>
            <totalOfferingAmount>7007000</totalOfferingAmount>
            <totalAmountSold>6006000</totalAmountSold>
            <totalRemaining>1001000</totalRemaining>
        </offeringSalesAmounts>
        <investors>
            <hasNonAccreditedInvestors>false</hasNonAccreditedInvestors>
            <totalNumberAlreadyInvested>12</totalNumberAlreadyInvested>
        </investors>
        <salesCommissionsFindersFees>
            <salesCommissions>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </salesCommissions>
            <findersFees>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </findersFees>
        </salesCommissionsFindersFees>
        <useOfProceeds>
            <grossProceedsUsed>
                <dollarAmount>0</dollarAmount>
                <isEstimate>true</isEstimate>
            </grossProceedsUsed>
        </useOfProceeds>
        <signatureBlock>
            <authorizedRepresentative>false</authorizedRepresentative>
            <signature>
                <issuerName>Syndax Pharmaceuticals Inc</issuerName>
                <signatureName>/s/ Joanna Horobin, M.D.</signatureName>
                <nameOfSigner>Joanna Horobin, M.D.</nameOfSigner>
                <signatureTitle>President and Chief Executive Officer</signatureTitle>
                <signatureDate>2010-08-04</signatureDate>
            </signature>
        </signatureBlock>
    </offeringData>
</edgarSubmission>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----