Planet of the Vampires (Italian: Terrore nello spazio, lit. 'Terror in Space'; released in the UK as The Demon Planet) is a 1965 science fiction horror film directed and co-written by Mario Bava, produced by Fulvio Lucisano, and starring Barry Sullivan and Norma Bengell. The screenplay was based on an Italian-language science fiction short story, Renato Pestriniero's "One Night of 21 Hours". The film follows the horrific experiences of the crew members of two giant spaceships that have crash landed on a forbidding, unexplored planet. The disembodied inhabitants of the world possess the bodies of the crew who died during the crash, and use the animated corpses to stalk and kill the remaining survivors.

The film was co-produced by Italian International Film and American International Pictures (AIP), with some financing provided by Spain's Castilla Cooperativa Cinematográfica. AIP released Planet of the Vampires as the supporting film on a double feature with Daniel Haller's Die, Monster, Die! (1965).

Years after its release, some critics have suggested that Bava's film was a major influence on Ridley Scott's Alien (1979) and Prometheus (2012), in both narrative details and visual design.