The Manster (双頭の殺人鬼, Sōtō no Satsujinki, "The Two-Headed Killer") is a 1959 American science-fiction horror film. Shot in Japan, it was produced by George P. Breakston and directed by Breakston and Kenneth G. Crane from a screenplay by Walter J. Sheldon. Sheldon's script was based on Breakston's story, which he originally titled The Split.

The film starred Peter Dyneley as a foreign correspondent in Japan who is given an experimental drug which causes an eye and eventually, a second head to grow from his shoulder. Tetsu Nakamura played the mad scientist, Dr. Suzuki, and Terri Zimmern his assistant, Tara. Jane Hylton also starred as Dyneley's wife.