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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-08-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100493</issuerCik>
        <issuerName>TYSON FOODS INC</issuerName>
        <issuerTradingSymbol>TSN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001088710</rptOwnerCik>
            <rptOwnerName>TYSON LIMITED PARTNERSHIP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2200 DON TYSON PARKWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SPRINGDALE</rptOwnerCity>
            <rptOwnerState>AR</rptOwnerState>
            <rptOwnerZipCode>72762</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>4.75% Tangible Equity Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2014-08-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>700000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>925960.0</value>
                    <footnoteId id="F2"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>700000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each 4.75% Tangible Equity Unit (TEU) includes a prepaid stock purchase contract that will automatically settle on July 15, 2017 (subject to postponement in certain limited circumstances) for between 1.0582 and 1.3228 shares of the Issuer's Class A common stock (subject to adjustment in certain circumstances), based upon the applicable market value of the Issuer's Class A common stock prior to settlement. The Reporting Person may elect to settle the purchase contracts prior to July 15, 2017 at the minimum settlement rate of 1.0582 shares of the Issuer's Common Stock, and the Issuer may elect to settle the purchase contracts prior to such date at the maximum settlement rate of 1.3228 shares of the Issuer's Class A common stock. The purchase contracts may also be settled early in connection with certain fundamental changes of the Issuer.</footnote>
        <footnote id="F2">Represents the maximum number of shares of the Issuer's Class A common stock initially issuable upon settlement of the purchase contracts included in the TEUs based on the maximum settlement rate.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Harry C. Erwin, III, General Partner</signatureName>
        <signatureDate>2014-08-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-08-05
0
0000100493
TYSON FOODS INC
TSN
0001088710
TYSON LIMITED PARTNERSHIP
2200 DON TYSON PARKWAY
SPRINGDALE
AR
72762
0
0
1
0
4.75% Tangible Equity Units
2014-08-05
4
J
0
700000
50
A
Class A Common Stock
925960.0
700000
D
Each 4.75% Tangible Equity Unit (TEU) includes a prepaid stock purchase contract that will automatically settle on July 15, 2017 (subject to postponement in certain limited circumstances) for between 1.0582 and 1.3228 shares of the Issuer's Class A common stock (subject to adjustment in certain circumstances), based upon the applicable market value of the Issuer's Class A common stock prior to settlement. The Reporting Person may elect to settle the purchase contracts prior to July 15, 2017 at the minimum settlement rate of 1.0582 shares of the Issuer's Common Stock, and the Issuer may elect to settle the purchase contracts prior to such date at the maximum settlement rate of 1.3228 shares of the Issuer's Class A common stock. The purchase contracts may also be settled early in connection with certain fundamental changes of the Issuer.
Represents the maximum number of shares of the Issuer's Class A common stock initially issuable upon settlement of the purchase contracts included in the TEUs based on the maximum settlement rate.
Harry C. Erwin, III, General Partner
2014-08-07