State Route 278 (SR 278, OH 278) is a north–south state highway located in tne southeastern part of the U.S. state of Ohio. The southern terminus of State Route 278 is at U.S. Route 50 approximately 4.75 miles (7.64 km) east of McArthur. The highway's northern terminus is at the T-intersection is has with State Route 595 nearly 5.50 miles (8.85 km) northwest of Nelsonville.

Established in the early 1930s, State Route 278 primarily connects rural communities in Vinton, Hocking, and Athens Counties. In Vinton County, it passes through and provides access to the Zaleski State Forest and Lake Hope State Park.

State Route 278 travels through portions of the counties of Vinton, Hocking and Athens. There are no segments of State Rouet 278 that are a part of the National Highway System.

When it debuted in 1930, State Route 278 was a spur route that ran along the segment of the current route between its current southern terminus at U.S. Route 50 and the village of Zaleski. In 1937, the highway was extended northerly from Zaleski, through Nelsonville up to its current northern terminus at State Route 595.