The ruling Serbian Progressive Party (SNS) has won a big parliamentary majority in the general election, vote monitors say.
Based on a partial count, the Cesid polling group said the centre-right party won almost 49% of the vote, or 157 seats in the 250-seat parliament.
The Socialists, coalition partners for the SNS, were running second with 15%.
SNS leader Aleksandar Vucic, 44, is now poised to become the country's next prime minister.
"They will have a majority" in parliament, Cesid chief Marko Blagojevic told reporters, referring to the SNS.
If confirmed, it will be the first time in Serbia's short democratic history that one party has won an overall majority in parliament.
The party's success in the polls is seen as driven by its anti-corruption campaign and by its move to start EU membership talks.
The opposition Democratic Party had been trailing third in the polls.
As polls closed at 19:00 GMT, election officials said the turnout was 50.3%, lower than the previous vote in 2012.
About 6.7 million voters were eligible to cast their ballots to choose a new 250-member parliament.
"We need a landslide victory to create new jobs, firmly pursue reforms and fight corruption with full forces," Mr Vucic said earlier this week.
His party is also credited with normalising relations with Kosovo.
It's a remarkable story of redemption for Aleksandar Vucic, who in his twenties served as information minister under the autocratic, ultra-nationalist president Slobodan Milosevic, says the BBC's Guy De Launey in Belgrade.
Yet now he's being trusted by voters to steer Serbia to membership of the European Union, he adds.
The opposition says it would be dangerous to place too much power in Mr Vucic.
"The whole country is mesmerised by this super-guy, Mr Vucic, who controls all the media and decides on everything. What we are facing now is a one-man regime," said Borko Stefanovic, the Democratic Party's parliamentary leader.
Serbia's next government will have plenty to do, our correspondent says. One in three Serbians cannot find a job, and the EU accession process will be long and rigorous.