Walter Pidgeon as Dr. Edward Morbius

Anne Francis as Altaira Morbius

Leslie Nielsen as Commander John J. Adams

Warren Stevens as Lt. 'Doc' Ostrow

Jack Kelly as Lt. Jerry Farman

Earl Holliman as Cookie

Richard Anderson as Chief Engineer Quinn

George D. Wallace as Bosun

Robert Dix as Crewman Grey

Jimmy Thompson as Crewman Youngerford

James Drury as Crewman Strong

Harry Harvey Jr. as Crewman Randall

Roger McGee as Crewman Lindstrom

Peter Miller as Crewman Moran

Morgan Jones as Crewman Nichols

Richard Grant as Crewman Silvers

James Best as Crewman (uncredited)

William Boyett as Crewman (uncredited)

Les Tremayne as Narrator (voice) (uncredited)

Frankie Darro as Robby the Robot (interior) (uncredited)

Marvin Miller as Robby the Robot (voice) (uncredited)