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."
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 center Dwight Howard and point guard Steve Nash, a two-time league Most Valuable Player, to their lineup.
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, while Nash and fellow-guard Kobe Bryant have been slowed by nagging injuries.
The poor start was particularly hard to swallow for the Lakers, who carried the NBA's largest payroll at just over $100 million.
The move came less than 48 hours after Lakers owner Jim Buss gave Brown a vote of confidence.