Komorowski took the oath of office at the Polish Parliament in Warsaw, the BBC reported.
Komorowski is Poland's fourth president since the fall of communism.
The Polish president has veto power and can make key government nominations, but the country's constitution gives most of the executive powers to the Cabinet.
Komorowski, a social conservative, ran as the candidate of the center-right party, Civic Platform, which supports the free market and is pro-European.
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