An optical connector adapter has a tubular sleeve having opposite open ends each for receiving a ferrule supporting an optical fiber to bring front end faces of the ferrules into contact with each other to optically connect together the optical fibers. An adapter housing supports therein the sleeve. The adapter housing has at least one elastically deformable engaging portion projecting from an outer peripheral surface portion of the adapter housing for detachable engagement directly to a mounting board or for detachable engagement to a mounting member detachably engageable with the mounting board to detachably mount the adapter housing to the mounting board.