<SEC-DOCUMENT>0001243786-16-000234.txt : 20160307
<SEC-HEADER>0001243786-16-000234.hdr.sgml : 20160307
<ACCEPTANCE-DATETIME>20160307184005
ACCESSION NUMBER:		0001243786-16-000234
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20160303
FILED AS OF DATE:		20160307
DATE AS OF CHANGE:		20160307

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MOSAIC CO
		CENTRAL INDEX KEY:			0001285785
		STANDARD INDUSTRIAL CLASSIFICATION:	AGRICULTURE CHEMICALS [2870]
		IRS NUMBER:				201026454
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		3033 CAMPUS DRIVE, SUITE E490
		CITY:			PLYMOUTH
		STATE:			MN
		ZIP:			55441
		BUSINESS PHONE:		7635772700

	MAIL ADDRESS:	
		STREET 1:		3033 CAMPUS DRIVE, SUITE E490
		CITY:			PLYMOUTH
		STATE:			MN
		ZIP:			55441

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	GLOBAL NUTRITION SOLUTIONS INC
		DATE OF NAME CHANGE:	20040401

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BRAUSEN ANTHONY T
		CENTRAL INDEX KEY:			0001253762

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-32327
		FILM NUMBER:		161489872

	MAIL ADDRESS:	
		STREET 1:		C/O THE MOSAIC COMPANY
		STREET 2:		3033 CAMPUS DRIVE, SUITE E490
		CITY:			PLYMOUTH
		STATE:			MN
		ZIP:			55441
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_145739399403891.xml
<DESCRIPTION>FORM 4
<TEXT>
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    <periodOfReport>2016-03-03</periodOfReport>

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    <issuer>
        <issuerCik>0001285785</issuerCik>
        <issuerName>MOSAIC CO</issuerName>
        <issuerTradingSymbol>MOS</issuerTradingSymbol>
    </issuer>

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            <rptOwnerCik>0001253762</rptOwnerCik>
            <rptOwnerName>BRAUSEN ANTHONY T</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O THE MOSAIC COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>3033 CAMPUS DRIVE, SUITE E490</rptOwnerStreet2>
            <rptOwnerCity>PLYMOUTH</rptOwnerCity>
            <rptOwnerState>MN</rptOwnerState>
            <rptOwnerZipCode>55441</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior VP -Finance</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

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            <exerciseDate>
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            <expirationDate>
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            <underlyingSecurity>
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            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
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            <conversionOrExercisePrice>
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            <exerciseDate>
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            <expirationDate>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
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                <underlyingSecurityShares>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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            <exerciseDate>
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            <expirationDate>
                <value>2023-07-18</value>
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            <exerciseDate>
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            <underlyingSecurity>
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            <conversionOrExercisePrice>
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                <footnoteId id="F5"/>
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            <expirationDate>
                <value>2024-03-07</value>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                <underlyingSecurityShares>
                    <value>10644.0</value>
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            </underlyingSecurity>
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                <underlyingSecurityTitle>
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                    <value>11658</value>
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                <directOrIndirectOwnership>
                    <value>D</value>
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                <value>Stock Option (Right to Buy)</value>
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                <value>28.49</value>
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            <transactionDate>
                <value>2016-03-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>23174</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
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                <value>2026-03-03</value>
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    </derivativeTable>

    <footnotes>
        <footnote id="F1">This Stock Option is 100% exercisable.</footnote>
        <footnote id="F2">One-for-One</footnote>
        <footnote id="F3">Not Applicable</footnote>
        <footnote id="F4">Grant Date 07/18/2013; option becomes exercisable in three equal installments commencing on the first anniversary of the grant date and on each anniversary thereafter.</footnote>
        <footnote id="F5">Grant Date 03/07/2014; option becomes exercisable in three equal installments commencing on the first anniversary of the grant date and on each anniversary thereafter.</footnote>
        <footnote id="F6">Grant Date 03/05/2015; option becomes exercisable in three equal installments commencing on the first anniversary of the grant date and on each anniversary thereafter.</footnote>
        <footnote id="F7">Grant Date 03/03/2016; option becomes exercisable in three equal installments commencing on the first anniversary of the grant date and on each anniversary thereafter.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Mark J. Isaacson, Attorney-in-Fact for Anthony T. Brausen</signatureName>
        <signatureDate>2016-03-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
