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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-01-03</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100885</issuerCik>
        <issuerName>UNION PACIFIC CORP</issuerName>
        <issuerTradingSymbol>UNP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001227314</rptOwnerCik>
            <rptOwnerName>HOPE RICHARDS JUDITH</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>PAUL HASTINGS JANOFSKY &amp; WALKER</rptOwnerStreet1>
            <rptOwnerStreet2>875 15TH STREET NW</rptOwnerStreet2>
            <rptOwnerCity>WASHINGTON</rptOwnerCity>
            <rptOwnerState>DC</rptOwnerState>
            <rptOwnerZipCode>20005</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>164</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>164</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6279</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Distribution ratio for Phantom Stock Units is 1:1.  End of period holdings include Phantom Stock Units granted prior to 8/15/96 which are exempt from Section 16 reporting.</footnote>
        <footnote id="F2">Phantom Stock Units are payable in cash only commencing at retirement.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>By: Michael M. Hemenway, Attorney-in-Fact  For: Judith Richards Hope</signatureName>
        <signatureDate>2006-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "edgardoc.xml", "description": "PRIMARY DOCUMENT", "secsgml_size_bytes": 3918}]
X0202
4
2006-01-03
0
0000100885
UNION PACIFIC CORP
UNP
0001227314
HOPE RICHARDS JUDITH
PAUL HASTINGS JANOFSKY & WALKER
875 15TH STREET NW
WASHINGTON
DC
20005
1
0
0
0
Phantom Stock
0
2006-01-03
4
A
0
164
0
A
Common Stock
164
6279
D
Distribution ratio for Phantom Stock Units is 1:1.  End of period holdings include Phantom Stock Units granted prior to 8/15/96 which are exempt from Section 16 reporting.
Phantom Stock Units are payable in cash only commencing at retirement.
By: Michael M. Hemenway, Attorney-in-Fact  For: Judith Richards Hope
2006-01-04