<SEC-DOCUMENT>0001209191-13-033249.txt : 20130621
<SEC-HEADER>0001209191-13-033249.hdr.sgml : 20130621
<ACCEPTANCE-DATETIME>20130621161307
ACCESSION NUMBER:		0001209191-13-033249
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20130619
FILED AS OF DATE:		20130621
DATE AS OF CHANGE:		20130621

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:		12390 EL CAMINO REAL
		STREET 2:		SUITE 150
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92130
		BUSINESS PHONE:		8585520866

	MAIL ADDRESS:	
		STREET 1:		12390 EL CAMINO REAL
		STREET 2:		SUITE 150
		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:			LIEF JACK
		CENTRAL INDEX KEY:			0001166280

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-32157
		FILM NUMBER:		13927254

	MAIL ADDRESS:	
		STREET 1:		ARENA PHARMACEUTICALS INC
		STREET 2:		6166 NANCY RIDER DRIVER
		CITY:			SAN DIEGO
		STATE:			CA
		ZIP:			92121
</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>2013-06-19</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001166280</rptOwnerCik>
            <rptOwnerName>LIEF JACK</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ARENA PHARMACEUTICALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>6166 NANCY RIDGE DRIVE</rptOwnerStreet2>
            <rptOwnerCity>SAN DIEGO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92121</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.50</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2013-06-19</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>62451</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2023-06-19</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>62451</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>62451</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This option vests and becomes exercisable in 12 substantially equal monthly installments on each monthly anniversary of June 19, 2013, subject to the reporting person's continued service with the issuer.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Patrick L. Keran, Attorney-in-Fact for Jack Lief</signatureName>
        <signatureDate>2013-06-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-24.4_478389
<SEQUENCE>2
<FILENAME>poa.txt
<DESCRIPTION>POA DOCUMENT
<TEXT>
LIMITED POWER OF ATTORNEY
FOR SECTION 16 REPORTING


	KNOW ALL PERSONS BY THESE PRESENTS, that the undersigned hereby makes,
constitutes and appoints Brian M. Culley, Patrick L. Keran and Brandi L.
Roberts, and each of them, as the undersigned's true and lawful attorney-in-fact
(the "Attorney-in-Fact"), with full power of substitution and resubstitution,
each with the power to act alone for the undersigned and in the undersigned's
name, place and stead, in any and all capacities to:

	1.	prepare, execute in the undersigned's name and on the undersigned's behalf,
and submit to the Securities and Exchange Commission ("SEC") a Form ID,
including amendments thereto, and any other documents necessary or appropriate
to obtain codes and passwords enabling the undersigned to make electronic
filings with the SEC of reports required or considered advisable under Section
16(a) of the Securities Exchange Act of 1934 (the "Exchange Act") or any rule or
regulation of the SEC;

	2.	prepare, execute and submit to the SEC, any national securities exchange or
securities quotation system and Mast Therapeutics, Inc. (the "Company") any and
all reports (including any amendment thereto) of the undersigned required or
considered advisable under Section 16(a) of the Exchange Act, and the rules and
regulations thereunder, with respect to the equity securities of the Company,
including Forms 3, 4 and 5; and

	3.	seek or obtain, as the undersigned's representative and on the undersigned's
behalf, information regarding transactions in the Company's equity securities
from any third party, including the Company and any brokers, dealers, employee
benefit plan administrators and trustees, and the undersigned hereby authorizes
any such third party to release any such information to the Attorney-in-Fact.

	The undersigned acknowledges that:

	1.	this Limited Power of Attorney authorizes, but does not require, the
Attorney-in-Fact to act at his or her discretion on information provided to such
Attorney-in-Fact without independent verification of such information;

	2.	any documents prepared or executed by the Attorney-in-Fact on behalf of the
undersigned pursuant to this Limited Power of Attorney will be in such form and
will contain such information as the Attorney-in-Fact, in his or her discretion,
deems necessary or desirable;

	3.	neither the Company nor the Attorney-in-Fact assumes any liability for the
undersigned's responsibility to comply with the requirements of Section 16 of
the Exchange Act, any liability of the undersigned for any failure to comply
with such requirements, or any liability of the undersigned for disgorgement of
profits under Section 16(b) of the Exchange Act; and

	4.	this Limited Power of Attorney does not relieve the undersigned from
responsibility for compliance with the undersigned's obligations under Section
16 of the Exchange Act, including, without, limitation, the reporting
requirements under Section 16(a) of the Exchange Act.

	The undersigned hereby grants to the Attorney-in-Fact full power and authority
to do and perform each and every act and thing requisite, necessary or
convenient to be done in connection with the foregoing, as fully, to all intents
and purposes, as the undersigned might or could do in person, hereby ratifying
and confirming all that the Attorney-in-Fact, or his or her substitute or
substitutes, shall lawfully do or cause to be done by authority of this Limited
Power of Attorney.

	This Limited Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 4 or 5 with respect to the
undersigned's holdings of and transactions in equity securities of the Company,
unless earlier revoked by the undersigned in a signed writing delivered to the
Attorney-in-Fact.

	This Limited Power of Attorney shall be governed and construed in accordance
the laws of the State of California without regard to conflict-of-law
principles.

	IN WITNESS WHEREOF, the undersigned has executed this Limited Power of Attorney
as of June 21, 2013.

Signature: /s/ Jack Lief

Printed Name: 	Jack Lief

</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
