Avram Grant has left West Ham following Sunday's 3-2 defeat at Wigan Athletic which sealed their relegation from the Premier Division.
The Hammers threw away a 2-0 lead to become the first team to go down from the top-flight this season.
"Avram Grant is no longer the manager of West Ham United," a statement said.
Kevin Keen, the first-team coach, will take charge of the club's final game of the season at home to Sunderland next Sunday.
After the match, Grant described the relegation as the "most sad day" of his career in football.
He said: "I'm also sorry for the supporters, the people in the club and the players.
"Maybe this game was the story of our season. It's a tough day."
Asked about his future, Grant added: "My future is not important now. All I care about is the commitment to the team and the fans.
"It's a big club and I'm sure they will back to the Premier League."
The Israeli has suffered back-to-back relegation following Portsmouth's demise last season.