<?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>0001019037</rptOwnerCik>
            <rptOwnerName>TYSON BARBARA</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>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-08-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>61</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>185917</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>4.75% Tangible Equity Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2014-08-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>30000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>39684.0</value>
                    <footnoteId id="F4"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>30000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of the Issuer's Class A Common Stock received by the Reporting Person pursuant to the Issuer's dividend reinvestment plan since the last Statement of Changes in Beneficial Ownership was filed by the Reporting Person. Such acquisitions are exempt from Section 16 reporting requirements pursuant to Rule 16a-11.</footnote>
        <footnote id="F2">Includes 15,523 shares of the Issuer's Class A Common Stock acquired by the Reporting Person pursuant to the Deferred Fee Plan for Directors, which shares shall vest 180 days after termination of the Reporting Person's service as a member of the Issuer's board of directors.</footnote>
        <footnote id="F3">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="F4">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>/s/ R.Read Hudson by Power of Attorney for Barbara Tyson</signatureName>
        <signatureDate>2014-08-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-08-05
0
0000100493
TYSON FOODS INC
TSN
0001019037
TYSON BARBARA
2200 DON TYSON PARKWAY
SPRINGDALE
AR
72762
1
0
0
0
Class A Common Stock
2014-08-05
4
J
0
61
0
A
185917
D
4.75% Tangible Equity Units
2014-08-05
4
J
0
30000
50
A
Class A Common Stock
39684.0
30000
D
Represents shares of the Issuer's Class A Common Stock received by the Reporting Person pursuant to the Issuer's dividend reinvestment plan since the last Statement of Changes in Beneficial Ownership was filed by the Reporting Person. Such acquisitions are exempt from Section 16 reporting requirements pursuant to Rule 16a-11.
Includes 15,523 shares of the Issuer's Class A Common Stock acquired by the Reporting Person pursuant to the Deferred Fee Plan for Directors, which shares shall vest 180 days after termination of the Reporting Person's service as a member of the Issuer's board of directors.
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.
/s/ R.Read Hudson by Power of Attorney for Barbara Tyson
2014-08-07