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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-02-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001477246</issuerCik>
        <issuerName>S&amp;W Seed Co</issuerName>
        <issuerTradingSymbol>SANW</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000899083</rptOwnerCik>
            <rptOwnerName>WYNNEFIELD PARTNERS SMALL CAP VALUE LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001251565</rptOwnerCik>
            <rptOwnerName>WYNNEFIELD PARTNERS SMALL CAP VALUE LP I</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001030806</rptOwnerCik>
            <rptOwnerName>WYNNEFIELD SMALL CAP VALUE OFFSHORE FUND LTD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001289453</rptOwnerCik>
            <rptOwnerName>Wynnefield Capital, Inc. Profit Sharing Plan</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001056835</rptOwnerCik>
            <rptOwnerName>WYNNEFIELD CAPITAL MANAGEMENT LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001251567</rptOwnerCik>
            <rptOwnerName>WYNNEFIELD CAPITAL INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001017043</rptOwnerCik>
            <rptOwnerName>OBUS NELSON</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001251568</rptOwnerCik>
            <rptOwnerName>LANDES JOSHUA</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>450 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 509</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-02-14</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18713</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.44</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>704385</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-02-14</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>29524</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.44</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1135610</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-02-14</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10964</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.44</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>278788</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-02-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1857</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.37</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>706242</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-02-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2930</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.37</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1138540</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-02-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1086</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.37</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>279874</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Wynnefield Partners Small Cap Value, L.P. (the &quot;Reporting Person&quot;) directly beneficially owns 706,242 shares of common stock, $0.0001 par value per share (&quot;Common Stock&quot;) of S&amp;W Seed Company.  Wynnefield Capital Management, LLC (&quot;WCM&quot;), as the sole general partner of the Reporting Person, has an indirect beneficial ownership interest in the shares of Common Stock that the reporting Person directly beneficially owns. WCM, located at the same address as the Reporting Person, is filing this Form jointly with the Reporting Person.  Nelson Obus and Joshua Landes as co-managing members of WCM have an indirect beneficial ownership interest in the shares of Common Stock that the Reporting Person directly beneficially owns.  Mr. Obus and Mr. Landes, each located at the same address as the Reporting Person, are filing this Form jointly with the Reporting person (see footnote 5).</footnote>
        <footnote id="F2">The Reporting Person has an indirect beneficial ownership interest in 1,138,540 shares of Common Stock, which are directly beneficially owned by Wynnefield Partners Small Cap Value, L.P. I (&quot;WPSCVI&quot;), as members of a group (a &quot;Group&quot;) under Section 13(d) of the Securities Exchange Act of 1934, as amended (the &quot;Exchange Act&quot;). WPSCVI, which maintains offices at the same address as the Reporting Person, is filing this Form jointly with the Reporting Person. WCM, as the sole general partner of WPSCVI, has an indirect beneficial ownership interest in the shares of Common Stock that WPSCVI directly beneficially owns.  Mr. Obus and Mr. Landes, as co-managing members of Wynnefield Capital Management, LLC, have an indirect beneficial ownership interest in the shares of Common Stock that WPSCVI directly beneficially owns.</footnote>
        <footnote id="F3">The Reporting Person has an indirect beneficial ownership interest in 279,874 shares of Common Stock, which are directly beneficially owned by Wynnefield Small Cap Value Offshore Fund, Ltd. (&quot;Offshore&quot;), as members of a Group. Offshore, located at the same address as the Reporting Person, is filing this Form jointly with the Reporting Person. Wynnefield Capital, Inc. (&quot;WCI&quot;), as the sole investment manager of Offshore, has an indirect beneficial ownership interest in the shares of Common Stock that Offshore directly beneficially owns. WCI, located at the same address as the Reporting Person, is filing this Form jointly with the Reporting Person.  Mr. Obus and Mr. Landes, as principal executive officers of WCI have an indirect beneficial ownership interest in the shares of Common Stock that Offshore directly beneficially owns.</footnote>
        <footnote id="F4">The Reporting Person has an indirect beneficial ownership interest in 99,235 shares of Common Stock, which are directly beneficially owned by Wynnefield Capital, Inc. Profit Sharing Plan (the &quot;Plan&quot;), as members of a Group.  The Plan, located at the same address as the Reporting Person, is filing this Form jointly with the Reporting Person. WCI, as the sole investment manager of the Plan, has an indirect beneficial ownership interest in the shares of Common Stock that the Plan directly beneficially owns. WCI, located at the same address as the Reporting Person, is filing this Form jointly with the Reporting Person. Mr. Obus and Mr. Landes, as principal executive officers of WCI have an indirect beneficial ownership interest in the shares of Common Stock that the Plan beneficially owns.</footnote>
        <footnote id="F5">Mr. Obus and Mr. Landes disclaim beneficial ownership of the securities described in this statement, except to the extent of their individual pecuniary interest in such securities.  The filing of this statement shall not be deemed an admission that Mr. Obus and Mr. Landes are, for purposes of Section 16 of the Exchange Act or otherwise, the beneficial owner of any securities specified in this statement.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>WYNNEFIELD PARTNERS SMALL CAP VALUE, L.P., By: Wynnefield Capital Management, LLC, General Partner, /s/ Nelson Obus, Managing Member</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>WYNNEFIELD PARTNERS SMALL CAP VALUE, L.P. I, By: Wynnefield Capital Management, LLC, General Partner, /s/ Nelson Obus, Managing Member</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>WYNNEFIELD SMALL CAP VALUE OFFSHORE FUND, LTD., By: Wynnefield Capital, Inc., /s/ Nelson Obus, President</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>WYNNEFIELD CAPITAL, INC. PROFIT SHARING PLAN, /s/ Nelson Obus, Authorized Signatory</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>WYNNEFIELD CAPITAL MANAGEMENT, LLC, /s/ Nelson Obus, Managing Member</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>WYNNEFIELD CAPITAL, INC., /s/ Nelson Obus, President</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Nelson Obus, Individually</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Joshua Landes, Individually</signatureName>
        <signatureDate>2017-02-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
