<SEC-DOCUMENT>0001659617-19-000101.txt : 20190715
<SEC-HEADER>0001659617-19-000101.hdr.sgml : 20190715
<ACCEPTANCE-DATETIME>20190715160442
ACCESSION NUMBER:		0001659617-19-000101
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20190711
FILED AS OF DATE:		20190715
DATE AS OF CHANGE:		20190715

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Foster Jonathan P.
		CENTRAL INDEX KEY:			0001545414

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-37758
		FILM NUMBER:		19955243

	MAIL ADDRESS:	
		STREET 1:		2450 SOUTH SHORE BLVD.
		STREET 2:		SUITE 402
		CITY:			LEAGUE CITY
		STATE:			TX
		ZIP:			77573

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Moleculin Biotech, Inc.
		CENTRAL INDEX KEY:			0001659617
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				474671999
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		5300 MEMORIAL DRIVE
		STREET 2:		SUITE 950
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77007
		BUSINESS PHONE:		713-300-5160

	MAIL ADDRESS:	
		STREET 1:		5300 MEMORIAL DRIVE
		STREET 2:		SUITE 950
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77007
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_156322106686428.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-07-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001659617</issuerCik>
        <issuerName>Moleculin Biotech, Inc.</issuerName>
        <issuerTradingSymbol>MBRX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001545414</rptOwnerCik>
            <rptOwnerName>Foster Jonathan P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MOLECULIN BIOTECH, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>5300 MEMORIAL DR., SUITE 950</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77007</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Exec. Vice President and CFO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>1.31</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-07-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>315000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2029-07-11</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>315000.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1161000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">(1) The stock option set forth in this table vests in four equal annual installments beginning on the first anniversary of the Transaction Date, subject to the grantee's continued service to the Company on each vesting date.</footnote>
        <footnote id="F2">(2) Issued in connection with the reporting person's employment with the Company.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Jonathan P. Foster</signatureName>
        <signatureDate>2019-07-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
