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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-10-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001171486</issuerCik>
        <issuerName>NATURAL RESOURCE PARTNERS LP</issuerName>
        <issuerTradingSymbol>NRP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001384938</rptOwnerCik>
            <rptOwnerName>Adena Minerals, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CLINE RESOURCE AND DEVELOPMENT COMP</rptOwnerStreet1>
            <rptOwnerStreet2>3801 PGA BOULEVARD, SUITE 903</rptOwnerStreet2>
            <rptOwnerCity>PALM BEACH GARDENS</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33410</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001384936</rptOwnerCik>
            <rptOwnerName>Foresight Reserves, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CLINE RESOURCE AND DEVELOPMENT COMP</rptOwnerStreet1>
            <rptOwnerStreet2>3801 PGA BOULEVARD, SUITE 903</rptOwnerStreet2>
            <rptOwnerCity>PALM BEACH GARDENS</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33410</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Owns entity w/ director right</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001384937</rptOwnerCik>
            <rptOwnerName>Insight Resource, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CLINE RESOURCE AND DEVELOPMENT COMP</rptOwnerStreet1>
            <rptOwnerStreet2>3801 PGA BOULEVARD, SUITE 903</rptOwnerStreet2>
            <rptOwnerCity>PALM BEACH GARDENS</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33410</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Owns entity w/ director right</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001384935</rptOwnerCik>
            <rptOwnerName>Cline Resource &amp; Development Co.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CLINE RESOURCE AND DEVELOPMENT COMP</rptOwnerStreet1>
            <rptOwnerStreet2>3801 PGA BOULEVARD, SUITE 903</rptOwnerStreet2>
            <rptOwnerCity>PALM BEACH GARDENS</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33410</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Owns entity w/ director right</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001385281</rptOwnerCik>
            <rptOwnerName>Cline Christopher</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CLINE RESOURCE AND DEVELOPMENT COMP</rptOwnerStreet1>
            <rptOwnerStreet2>3801 PGA BOULEVARD, SUITE 903</rptOwnerStreet2>
            <rptOwnerCity>PALM BEACH GARDENS</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33410</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Owns entity w/ director right</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Units</value>
            </securityTitle>
            <transactionDate>
                <value>2012-10-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>6049155</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10596917</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">On October 2, 2012, Adena Minerals, LLC (&quot;Adena&quot;) effected an in-kind distribution of 6,049,155 common units (the &quot;Distributed Units&quot;) to its sole member, Foresight Reserves, L.P. (&quot;Foresight&quot;), for no additional consideration.  Foresight immediately thereafter effected an in-kind distribution of all of the Distributed Units to its direct and indirect owners (including the distribution of 1,980,156 of the Distributed Units to Christopher Cline), for no additional consideration.</footnote>
        <footnote id="F2">Adena Minerals, LLC holds 10,596,917 common units of record.  Foresight is the sole member of Adena, and Insight Resource, LLC (&quot;Insight&quot;) is the general partner of Foresight. Cline Resource and Development Company is the managing member of Insight and Christopher Cline is the sole shareholder and sole director of Cline Resource and Development Company.  Accordingly, each of Christopher Cline, Cline Resource and Development Company, Insight, Foresight and Adena are deemed to share voting and dispositive control with over the common units held of record by Adena.</footnote>
    </footnotes>

    <remarks>Adena may be deemed to be a director for purposes of this Form by virtue of its right to nominate two directors to the board of GP Natural Resource Partners LLC, the general partner of NRP (GP) LP, which is the general partner of Natural Resource Partners LP.

The distribution of 1,980,156 common units to Christopher Cline is reflected on a Form 4 filed by Mr. Cline on 10/02/2012.

Adena Minerals, LLC
By: Foresight Reserves, L.P., its Managing Member
By: Insight Resources, LLC, its General Partner
By: Cline Resource and Development Company, its Managing Member

/s/ Christopher Cline,

Foresight Reserves, L.P.
By: Insight Resources, LLC, its General Partner
By: Cline Resource and Development Company, its Managing Member

/s/ Christopher Cline

Insight Resources, LLC, its General Partner
By: Cline Resource and Development Company, its Managing Member

/s/ Christopher Cline

Cline Resource and Development Company

/s/ Christopher Cline

Christopher Cline

/s/ Christopher Cline</remarks>

    <ownerSignature>
        <signatureName>/s/ Christopher Cline, Authorized Representative</signatureName>
        <signatureDate>2012-10-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
