The Franklin O-300 (company designation 6AC-298) was an American air-cooled aircraft engine of the early 1940s. The engine was of six-cylinder, horizontally-opposed layout and displaced 300 cu in (5 L). The power output ranged between 130 hp (97 kW) and 175 hp (130 kW) depending on variant. The 6ACG-298 featured a geared propeller drive.
An enlarged displacement version was known as the O-315, 6A3 or 6AL-315.