Civic Platform won 25 seats out of 50 seats given to Poland in the 736-member European Parliament, the Polish electoral commission said.
The opposition Law and Justice party won 27.41 percent, the leftist Democratic Alliance and Labor Party won 12.33 percent, and the Polish Peasants party 7.03 percent.
Pawel Swieboda, head of the Warsaw think-tank DemosEuropa, said Civic Platform will strengthen its influence within the center-right European People's Party, or EPP, that remains the largest bloc in the European Parliament, Poland's thenews.pl Web site reported.
Poland's turnout Sunday was 24.5 percent and was among the lowest in the European Union countries.
About 30 million Poles were eligible to vote.