The ruling Socialists have become Portugal's largest party in the European Parliament, but without taking a majority of the seats.
A high profile campaign by the former president Mario Soares gave his party 43% of the vote and a 12 point lead over the main opposition party the Social Democrats.
Commentators have expressed surprise that despite the participation of the popular Mr Soares, the campaign attracted little interest among voters.
The Social Democrats' vice-president Antonio Capucho said: "The 'Mario Soares' operation did not work. Abstentions again reached worrying levels."
Turnout in Portugal was around the same level as in the previous election at 40%.
The anti-European party - the Popular Party - achieved a much stronger showing than expected and will send two members to Strasbourg after winning 8% of the vote.
This election result could stand the Socialists in good stead in the run-up to October's general election.