About 10,000 police officers gathered near the rally in front of the state parliament in downtown Belgrade to prevent it from turning violent, as similar protests by right-wing protesters have in the past.
The former allies of the late autocratic leader Slobodan Milosevic want Serbia's government to schedule early elections because of the country's rising poverty and unemployment and falling living standards. They also accuse the government of corruption.
The nationalists are promising economic recovery, higher salaries and new jobs, if they come to power. They have risen in popularity amid Serbia's economic turmoil triggered by the global recession and the slow pace of the country's integration into the European Union - the government's main political goal.
"For 10 years, Serbia has lived under a corrupt and incapable government," Serbian Progressive Party leader Tomislav Nikolic told the rally, as the crowd chanted "Thieves! Thieves!" and "Changes! Changes!"
"We will save Serbia when we take over," he said. "No one can stop us."
Opposition leaders addressing the crowd - estimated by police at about 55,000 - threatened to blockade the capital if their demands to move parliamentary elections forward from 2012 are not met within the next two months.
The spokeswoman for ruling Democratic Party, Jelena Trivan, said there will be no early elections despite the protest.
"If they have any concrete suggestions for the resolution of the crisis, the government is willing to talk," she said. "But, early elections are held when the government loses a majority in the parliament, which is not the case."
Nikolic's party which organized the rally said afterward that the size of the gathering showed that "people want elections, a better life and a more responsible and capable government."
It said that if authorities don't respond to the call for the early elections, "even more people will gather" in the capital in April and remain protesting until their demands are met.
"This is the last warning to the government," said another opposition leader, Velimir Ilic. "We don't want to do it like in Egypt or Tunisia. We just want elections."
Milosevic, who died in 2006 during his genocide trial at the U.N. war crimes tribunal in The Hague, Netherlands, was ousted in 2000 after massive street protests in Belgrade led by officials from the current Serbian government.
"This is the start of a counterrevolution," said Milos Joksimovic, a 35-year-old mechanical engineer who took part in the anti-Milosevic demonstrations at the same spot in the capital in October 2000. He spoke as he watched Saturday's rally from a distance.
"They are becoming very strong, and it's scary," he said.
After the rally, police detained about 20 football fans who were chanting anti-government slogans.
Jovana Gec contributed to this report.