Just 43.1 percent of the eligible 375 million Europeans participated during four days of voting, Thursday through Sunday, early results indicated, the EUobserver reported Monday.
The result was more than 2 points lower than in 2004, when 45.5 percent turnout was the lowest in the parliament's history, election officials said.
Besides Belgium and Luxembourg, where voting was mandatory and turnout topped 90 percent, Malta reported the highest number of voters, initial tabulations by TNS Sofres for the European Parliament indicated. Other countries where a majority of people voted included Italy, Denmark, Greece, Cyprus and Latvia.
Slovakia had the lowest turnout, with only 19.6 percent of eligible voters turning out, compared to 17 percent in its first EU election in 2004. Lithuania had the second-lowest turnout with 20.5 percent in its second election.
"I don't know why (the turnout is so low) and we need to study why people don't go out and vote," Liberal leader Graham Watson said.
"We have to increase turnout if we can," said outgoing parliament president Hans-Gert Poettering of the conservative European People's Party-European Democrats.
Poettering said increasing voter turnout didn't mean returning to the system when European Parliament members were appointed by national parliaments.