The Thunder is 1-12, worst in the NBA.
Assistant coach Scott Brooks was named interim coach.
The Thunder dropped their 10th straight game on Friday night, a 105-80 home loss to the New Orleans Hornets.
Carlesimo accompanied the Thunder when they moved to Oklahoma City from Seattle before this season. He was 21-74 in 95 games as the team's coach.
In eight seasons as an NBA coach with Portland, Golden State, Seattle and Oklahoma City, Carlesimo has a career record of 204-296 in 500 regular season games.