<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2017-04-17</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001279704</issuerCik>
        <issuerName>Cellectar Biosciences, Inc.</issuerName>
        <issuerTradingSymbol>CLRB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001704021</rptOwnerCik>
            <rptOwnerName>Friend John E. II</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CELLECTAR BIOSCIENCES, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>3301 AGRICULTURE DRIVE</rptOwnerStreet2>
            <rptOwnerCity>MADISON</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53716</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP, Chief Medical Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <remarks>Exhibit List  Exhibit 24 - Power of Attorney</remarks>

    <ownerSignature>
        <signatureName>/s/ Chad Kolean, attorney-in-fact for John E. Friend II</signatureName>
        <signatureDate>2017-04-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
