Sousa, who was previously in charge of Poland, had a two-year contract with the Rio de Janeiro giants.
Flamengo said on its social media channels that his staff had also left the club. Brazilian media are reporting that Ceará's Dorival Junior will be the new coach.
Flamengo, which is 14th in the Brazilian championship with 12 points from 10 matches, decided to fire Sousa after a 1-0 loss at Red Bull Bragantino on Wednesday.
The 51-year old Sousa left Poland last year when his contract was terminated by the national soccer federation.
Sousa's career also includes stints at England's Leicester and Queens Park Rangers, France's Bordeaux and Italy's Fiorentina.
