Assistant coach Bernie Bickerstaff will take over as interim head coach for Friday's game against the Golden State Warriors and a search for a new head coach will begin immediately, general manager Mitch Kupchak said.
"This was a difficult and painful decision to make," Kupchak said in a statement posted on the team's website.
"Mike was very hard-working and dedicated, but we felt it was in the best interest of the team to make a change at this time. We appreciate Mike's efforts and contributions and wish him and his family the best of luck."
Brown, who previously coached the Cleveland Cavaliers and LeBron James, was in the second year of a four-year, $18 million deal, of which the final year was not fully guaranteed.
He became the first NBA coach fired after five or fewer games of a season since Dolph Schayes of the Buffalo Braves resigned after one game of the 1971-72 season, ESPN reported.
The move came less than 48 hours after Lakers owner Jim Buss gave Brown a vote of confidence.
"I have great respect for the Buss family and the Lakers' storied tradition and I thank them for the opportunity they afforded me," Brown said in a statement.
"I have a deep appreciation for the coaches and players that I worked with this past year and I wish the organization nothing but success as they move forward."
The Lakers stand behind only the Boston Celtics, with 17 NBA crowns, on the league's championship list. Next on the list is the Chicago Bulls with six.
The disappointing start by the Lakers, who had the worst record in the Western Conference, followed an off-season in which the NBA team added All-Star centre Dwight Howard and point guard Steve Nash, a two-time league Most Valuable Player, to their line-up.
Last season, the Lakers won the Pacific Division with a 41-25 record and reached the conference semi-finals before falling to eventual conference champions Oklahoma City Thunder in five games.
The Lakers, hobbled by injuries in the early season, had struggled under a new offensive system installed by Brown.
Howard is still recovering his form after back surgery that ended his 2011-12 season, Nash has missed the last three games due to a leg injury, and 14-time All-Star Kobe Bryant has been slowed by a foot injury.
The poor start was particularly hard to swallow for the Lakers, who carried the NBA's largest payroll at just over $100 million.
Lakers Hall of Famer Magic Johnson, who like Bryant won five NBA rings with the Lakers, reacted to Brown's firing on Twitter.
"Feel bad for Coach Mike Brown, who's a great guy, but don't think he was the right guy for the job in the first place," Johnson said.
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