<SEC-DOCUMENT>0001209191-16-090227.txt : 20160106
<SEC-HEADER>0001209191-16-090227.hdr.sgml : 20160106
<ACCEPTANCE-DATETIME>20160106210832
ACCESSION NUMBER:		0001209191-16-090227
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20160104
FILED AS OF DATE:		20160106
DATE AS OF CHANGE:		20160106

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Mast Therapeutics, Inc.
		CENTRAL INDEX KEY:			0001160308
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				841318182
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		3611 VALLEY CENTRE DRIVE
		STREET 2:		SUITE 500
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92130
		BUSINESS PHONE:		8585520866

	MAIL ADDRESS:	
		STREET 1:		3611 VALLEY CENTRE DRIVE
		STREET 2:		SUITE 500
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92130

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ADVENTRX PHARMACEUTICALS INC
		DATE OF NAME CHANGE:	20030613

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	BIOKEYS PHARMACEUTICALS INC
		DATE OF NAME CHANGE:	20010928

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			EMANUELE ROBERT MARTIN
		CENTRAL INDEX KEY:			0001184991

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-32157
		FILM NUMBER:		161328671
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc4.xml
<DESCRIPTION>FORM 4 SUBMISSION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-01-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001160308</issuerCik>
        <issuerName>Mast Therapeutics, Inc.</issuerName>
        <issuerTradingSymbol>MSTX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001184991</rptOwnerCik>
            <rptOwnerName>EMANUELE ROBERT MARTIN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3611 VALLEY CENTRE DRIVE, SUITE 500</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN DIEGO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92130</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior VP, Development</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.42</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-01-04</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>572700</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2026-01-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>572700</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>572700</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This option vests and becomes exercisable in 48 substantially equal monthly installments on each monthly anniversary of January 4, 2016, subject to the reporting person's continued service with the issuer.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ R. Martin Emanuele</signatureName>
        <signatureDate>2016-01-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
