After a specially convened board meeting on Monday, Roberts, 39, was released from his post after six years at the club as player and manager.
Roberts' assistant Andy Millen has been put in caretaker charge until a new manager is appointed.
The Somerset Park club, who are second bottom of Scottish League One, hope to have a new boss in place by 6 January.
after taking over from Brian Reid.
Ayr United have sacked manager Mark Roberts with the team winning only one of their last 11 matches.