- Protesters denounce corruption and demand the impeachment of President Dilma Rousseff
- They march in key cities: Sao Paulo, Rio de Janeiro and the capital, Brasilia
Her administration is struggling amid a weak economy and a massive corruption scandal involving the country's state-run oil company.
"I love Brazil. I love my country. And I am tired of corruption. We are tired of corruption. It doesn't matter which political party you are from, we are tired of being robbed," a protester told CNN in Sao Paulo, where people packed the main Paulista Avenue.
In Rio de Janeiro, they gathered along Copacabana beach, while in the capital, Brasilia, protesters marched on government headquarters.
The mood was festive. Many demonstrators wore the country's colors -- green, blue and yellow -- waved flags, and chanted: "Out Dilma."
Amid complaints about the economy, protesters say they are incensed because Brazilian investigators are unraveling a huge money-laundering and bribery case centered around Petrobras, the country's national oil company. Dozens of politicians, some in Rousseff's party, are accused of accepting millions in payments.
The President has not been implicated in the investigation, but she was the Energy Minister and chairwoman of Petrobras during much of the time that the alleged corruption took place.
Sunday night Rousseff sent two of her ministers to address the nation at a televised press conference. The justice minister and the general secretary said that the government was listening and would announce changes in several days designed to combat corruption.
The announcement did little to quiet the protests in some cities. Many protesters banged pots and pans and honked car horns.
CNN iReporter Bruno Teles with Avant Drones shot aerial footage of the crowds in Sao Paulo. He said, "Brazilians are tired of such corruption, lies and [the] bad economy."
Before becoming the country's first female president in 2011, Rousseff, from the Workers' Party, was chief of staff to former President Lula da Silva. She won re-election in October, in one of the tightest races in recent years, but has since seen her approval rate plummet along with the economy.
Brazil is headed into recession again this year, inflation is up and the currency is at a 12-year low.
Rousseff's approval rating down to 23% from 42% at the end of 2014, according to DataFolha. The economy is expected to contract this year and the real has plummeted 23% against the dollar.