State Route 308 (SR 308, OH 308) is a north–south state highway in the central portion of Ohio, a U.S. state. The southern terminus of State Route 308 is at State Route 229 in the western end of the village of Gambier, and its northern terminus is 3 miles (4.8 km) to the north of that point at a T-intersection with U.S. Route 36 that is located approximately 1.5 miles (2.4 km) east of the city limits of Mount Vernon.

State Route 308 runs exclusively in the central portion of Knox County. The route is not a part of the National Highway System, a system of highways deemed most important for the economy, mobility and defense of the nation.

When first designated in 1932, State Route 308 was a spur route connecting U.S. Route 36 with the village of Gambier and Kenyon College. It would be 1939 before State Route 308 would become a connector route, when State Route 229 was extended east of Mount Vernon, and in the process connected with State Route 308 at its southern terminus.

The entire route is in Knox County.