Mark McGhee has parted company with Aberdeen, the Clydesdale Bank Premier League club have confirmed.
The 53-year-old has found himself under increasing pressure following a run of poor results but had recently been given a vote of confidence by the Pittodrie board.
His assistants Scott Leitch and Colin Meldrum have also left the club, with the Dons now sitting second bottom of the Clydesdale Bank Premier League.
Chairman Stewart Milne said: "On behalf of everyone at the club, I would like to thank Mark, Scott and Colin for their time at Aberdeen.
"It goes without saying that everyone at Aberdeen Football Club wishes Mark, Scott and Colin every success in the future."
Milne will begin the search for a new manager immediately but "without any timescale being set on the appointment".
Details of interim arrangements are set to be announced shortly.
Aberdeen have suffered defeat in their last six games in the SPL, including the 9-0 thrashing to Celtic last month - a club record defeat.
The Dons were set to face Celtic again this weekend, before all SPL games were postponed as a result of severe weather conditions.