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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 H3EcFX21dPvCBFex/8JsvqWTewyk6rd/c2A2KcOBP+k7jlZ1lDHqcht/+KVN3yCd
 LgRCJErslWVrGFLMMJdKrg==

<SEC-DOCUMENT>0001179110-09-016987.txt : 20091215
<SEC-HEADER>0001179110-09-016987.hdr.sgml : 20091215
<ACCEPTANCE-DATETIME>20091215200815
ACCESSION NUMBER:		0001179110-09-016987
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20091211
FILED AS OF DATE:		20091215
DATE AS OF CHANGE:		20091215

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			LEVRAN ALEXANDER
		CENTRAL INDEX KEY:			0001222006

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-29454
		FILM NUMBER:		091243059

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			POWER ONE INC
		CENTRAL INDEX KEY:			0001042825
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRONIC COMPONENTS, NEC [3679]
		IRS NUMBER:				770420182
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		740 CALLE PLANO
		CITY:			CAMARILLO
		STATE:			CA
		ZIP:			93012
		BUSINESS PHONE:		8059878741

	MAIL ADDRESS:	
		STREET 1:		740 CALLE PLANO
		CITY:			CAMARILLO
		STATE:			CA
		ZIP:			93012
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-12-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001042825</issuerCik>
        <issuerName>POWER ONE INC</issuerName>
        <issuerTradingSymbol>PWER</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001222006</rptOwnerCik>
            <rptOwnerName>LEVRAN ALEXANDER</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>740 CALLE PLANO</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMARILLO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>93012</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr. VP Res. &amp; Dev., CTO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-12-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>75000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>239299</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents restricted stock units which vest in three equal annual installments commencing on December 11, 2010.</footnote>
        <footnote id="F2">Granted as compensation for services.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Tina D. McKnight, Attorney-in-Fact for Alexander Levran</signatureName>
        <signatureDate>2009-12-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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