Demonstrators from both ends of Brazil's political spectrum briefly clashed in Rio, where left-wing protesters came to blows with a group commemorating 50 years since the military coup.
Right-wing elements in Rio on Saturday called for a re-enactment of the 1964 "March of Families for God and Freedom", which came just days before a military coup that lasted until democracy's restoration in 1985.
Left-wing groups arranged a counter-demonstration and, despite a heavy police presence, several people broke through police lines and clashed in the city centre.
Their opponents, numbering about 300, were at pains not to praise the dictatorship. They however said the current president, Dilma Rousseff, who as a left-wing activist suffered torture under the military junta, was leading the country to ruin.
"Democracy doesn't exist in Brazil - we don't have a majority but a slew of minorities, such as Indians and feminists, with Dilma in charge," an activist, Felipe Paulomo, told the AFP news agency.
Among left-wing protesters,, one woman who gave her name as Hannah carried a cardboard sign reading: "Never again dictatorship - fascists out."
She told AFP: "Here come the torturers again, lessons not learned from the deaths their parents caused."
Historians estimate about 400 dissidents were killed under 21 years of military rule.
More than 2,000 people meanwhile demonstrated in Sao Paulo, warning of fighting at the forthcoming football World Cup.
Last June, the Brazilian government was stunned when more than a million people demonstrated against the cost of the World Cup and the Rio Olympics, in a country which suffers from corruption and poor infrastructure.
This year has seen smaller but sometimes violent protests. Some protesters have vowed to fuel more unrest during the June-July football tournament.