Gun Frontier (ガン フロンティア, Gan Furontia) is a 1972 manga by Leiji Matsumoto. It introduces Tochiro Oyama, best friend to Matsumoto's classic hero, Captain Harlock, who is in turn depicted as a gunslinger in the Old West. In sharp contrast to other Matsumoto's stories, Gun Frontier is a comedy adventure rather than a space opera. Also, unlike other Harlock stories, in Gun Frontier, Harlock is depicted as Tochiro's sidekick.

It is a harsh and barren wasteland, where the weak aren't allowed to dream. It is also a sacred land for true men, for there is no place a man can feel more alive. This is the Gun Frontier. Sea Pirate Captain Harlock and the errant samurai, Tochiro arrive in the United States on the Western Frontier. Along with a mysterious woman they meet along the way, the two friends challenge sex rings, bandits, and corrupt sheriff. They are searching for a lost clan of Japanese immigrants, and they will tear Gun Frontier from end to end until they find it.

Since the original manga, there has been a novel and a 2002 anime adaption of the series.