Tetsuo Okamoto, who had won Brazil's first Olympic medal of swimming, died at the age of 75 in the city of Marilia, in the state of Sao Paulo.
Okamoto, a Brazilian of Japanese descendants, took a bronze medal in 1, 500 meters freestyle of the 1952 Helsinki Olympic Games.
He was also a double bronze medalist in 400 and 1,500 meters freestyle of the 1951 Buenos Aires Pan American games.
He died of respiratory insufficiency, reported the local news agency Agencia Estado.
The Brazilian Aquatic Sports Confederation has decreed a 3-day official mourning and one minute of silence before the start of the forthcoming competitions in Brazil.