Fueled by mounting anger over a corruption scandal that has implicated politicians in Rousseff's party, demonstrators chanted "Out with Dilma" and "Time for change."
Police estimated that 275,000 demonstrators marched in Sao Paulo. A sea of protesters dressed in the green and yellow of the Brazilian flag used decades-old rallying cries to fire up their ranks, singing rock songs that date back to protests of the country's one-time military dictatorship.
It's the second day of nationwide anti-government demonstrations in less than a month. And protesters vowed that it wouldn't be the last.
There are a number of issues at play
. One of the biggest: an investigation into a multimillion-dollar kickback scheme at the state-run oil company Petrobras.
Most of the politicians accused in the investigation belong to Rousseff's Workers Party and its allies.
And during many of the years that the alleged corruption took place, Rousseff was the chairwoman of Petrobras. There hasn't been any evidence she was involved with the scheme, and her supporters say the position is merely a figurehead.
Rousseff has defended Brazilians' right to protest and acknowledged the need to clean up corruption at Petrobras but denied any prior knowledge of the alleged kickback scheme.
Brazilians are still outraged.
Rousseff won re-election with just over 50% of the votes in October, but her approval rating plummeted to 13% after protests began last month.
"Many things have changed since the election," Janaina, a protester in Sao Paulo, said on Sunday, noting that even some people who voted for Rousseff were in the crowd.
Some protesters said they'd rather see Rousseff step down than push for impeachment, which could be difficult to push through without evidence tying the President directly to the corruption scandal.
But Janaina said impeachment remained a realistic option.
"Yes, it has to be," she said. "It's our last hope."