Waving Serbian flags, the supporters of the Serbian Progressive Party (SNS), Serbia's main opposition force, carried placards saying "We fight for changes" and shouted "Thieves" at any mention of President Boris Tadic.
"They do not care about your living conditions," Tomislav Nikolic, the SNS leader and Tadic's opponent at the presidential polls, told the crowd.
"If they had cared, they would have done something to decrease the unemployment and attract investors," he said.
Some 24 percent of Serbia's population of 7.4 million is unemployed, according to official data. The country has relied heavily on foreign investments in the past years, but the global economic crisis has slowed the trend.
If elected, Nikolic said he would carry out a tax reform while increasing the pensions and enabling further investments notably in agriculture and industry.
"If you want a real change, vote for us," he said.
Serbia holds local, regional, parliamentary and presidential elections on May 6.
Latest surveys showed that the SNS, former hardline nationalists who have since turned towards conservative populism, can expect to win 33.5 percent of the votes while Tadic's party would get 28.3 percent.
Nikolic and Tadic are neck-and-neck in the presidential race, with 36.1 and 35.7 percent in the first round on May 6, facing a run-off two weeks later, the results showed.
Analysts estimate that Tadic will win the presidential race in the run-off.