The Mars Automatic Pistol, also sometimes known as the Webley-Mars, was a semi-automatic pistol developed in 1900 by the Englishman Hugh Gabbet-Fairfax and distributed by the Mars Automatic Pistol Syndicate Ltd. of Birmingham. It was manufactured first by Webley & Scott and later by small gunmakers in Birmingham and London. Manufacture ceased in 1907.

The Mars Automatic Pistol is noted for being available in a variety of 8.5 mm, 9 mm and .45 calibres. These were all bottlenecked cartridges with a large charge of powder, making the .45 version the most powerful handgun in the world for a time. It used a unique long recoil rotating bolt action which ejected spent cartridges straight to the rear, and the feed mechanism is unusual in that it pulls cartridges backwards out of the magazine and then lifts them up into the breech face.