His firing was first reported by ESPN.
Team officials have scheduled a news conference for later in the afternoon Monday.
"These decisions are never easy, and this one is especially tough because Alvin and I had a very good working relationship," said Clippers Vice President of Basketball Operations Elgin Baylor. "But I reached the conclusion Sunday night that the players simply were not responding and I believe a change is necessary at this time."
In two-plus seasons with the Clippers, Gentry was 89-133. Thus far this season, the Clippers are 19-39 and have dropped 12 of their last 15 games.
They have dropped five straight, and 14 of 17, and at 19-39, are last in the NBA's Pacific Division.
Gentry has faced criticism nearly the entire season, failing to motivate a team that is facing a number of offseason questions.
"I do believe we have good people and good players on this team," Gentry said in a statement. "I think the players must try to make something positive out of the remainder of the season."
After acquiring point guard Andre Miller prior to the start of this season, expectations were raised, possibly higher than they should have been. The team has struggled from the start and has been unable to compete in the highly competitive Western Conference.
Assistant Coach Dennis Johnson will replace Gentry. His first game will be Monday night against New Orleans.
Johnson is in his fourth season with the Clippers' coaching staff. He joined the team as an assistant coach midway through the 1999-2000 season after beginning his professional head-coaching career earlier that season with the CBA's La Crosse Bobcats.