Sunday's turnout was less than half the level registered in January 2012 when two thirds of Croatians voted in a referendum to join the European Union after years of difficult reforms required by Brussels.
Six of Croatia's 12 seats in the 754-member Strasbourg-based parliament went to the Croatian Democratic Union (HDZ). It lost office late in 2011 to the leftist Social Democratic Party (SPD) which gained five seats in Sunday's poll.
The remaining seat went to the opposition Labor Party, according to preliminary results released by Croatia's State Electoral Commission.
Pre-vote surveys had suggested that the SPD would win the majority of Croatia's allocation of seats in Strasbourg.
Prime Minister Zoran Milanovic, speaking in Zagreb, highlighted the unique nature of Sunday's vote: "These are the first European elections in Croatia's history."
Political analyst Zarko Puhovshi said turnout among 3.7 million eligible voters was low because Croatians thought Sunday's poll was unimportant.
"Instead of an election campaign, we had weeks of virtual electoral silence," he said, referring to politicians reluctance to campaign on EU-related issues amid rare media debates.
Another factor was the short term of those elected. Croatia's 12 European Parliament representatives will only serve for one year.
In 2014, Europe-wide elections will be held to choose a new European Parliament to represent the EU's 500 million citizens for the following five years.
Croatia, which has endured domestic economic woes, will be only the second of six former Yugoslav republics to join the EU. Slovenia joined the bloc in 2004.
The HDZ party ran Croatia for most of the period since the early 1990s when the nation achieved independence during the violent break up of former Yugoslavia.
ipj/mz (APF, AP)