At least 54 people were killed in Teresopolis about 62 miles (100 km) north of Rio, the town's mayor said, after hillsides and riverbanks buckled under the equivalent of a month's rainfall in 24 hours.
At least 16 other people were killed in two other towns in the region, officials with the government's Civil Defense agency said.
The rains sweeping southeastern Brazil also killed 13 people in Sao Paulo state on Tuesday and snarled transport in the country's financial capital.
The death toll was expected to rise, with about 50 people believed missing just in Teresopolis, mayor Jorge Mario told Globo television.
"There are 48 dead, and that number will rise because rescue teams are still arriving in the areas that have been worst affected," he said, adding that about 1,000 people had been left homeless.
"It's the biggest catastrophe in the history of the town."
Thousands of people in the picturesque area, known as the Serrana region, were isolated by the flood waters and cut off from power and telephone contact.
The downpour caused at least one river to burst its banks, submerging cars and destroying houses in Teresopolis, television images showed.
