The polls are expected to provide a tight race between ultranationalists and pro-Western reformers.
Residents of Serbia's capital Belgrade were going to the polls with hopes that their situation would improve.
"I hope these elections bring changes for the better, democratic changes and more prosperity," one woman told Reuters television.
Opinion surveys show the race is too close to call. The ultranationalist Serbian Radical Party and the pro-Western Democratic Party are each polling about 30 percent, not enough to form a government on their own.
Prime Minister Vojislav Kostunica's Democratic Party of Serbia is in third place and seen as the kingmaker, equally likely to support either of its rivals in forming a government.
The United Nations is expected to rule this year on the fate of the breakaway province of Kosovo. The West favors granting independence to its majority ethnic Albanian population as they have demanded since 1999, when NATO bombs drove out Serb forces accused of killing civilians while fighting an insurgency.
Kosovo A Hot Topic
High turnout is expected among minority Serbs living in Kosovo, as many perceive the election as the last chance to express their political preferences while Kosovo is still part of Serbia.
"I cast my vote so that politicians I hope will make our lives better win," Zivojin Mikic, a Serbian pensioner living in Kosovo, told Reuters. "I voted for us not to be scattered away. I voted for No. 4 (Serbian Radical Party)."
Another pensioner, Predrag Nikolic, said he voted for the Socialists.
"I have voted for the Socialist Party, for Ivica Dacic, because I think that they are good,," Nikolic said. "I expect a better life out of this election."
However, all the major Serbian political parties -- except the Democratic Party of President Boris Tadic favored by the West -- say they will not accept the loss of Kosovo. Tadic is telling the Serbs that this move simply might be inevitable.
About 6.6 million Serbians are entitled to vote. The first projections of the result are expected before midnight, local time.