State Route 339 (SR 339) is a north–south state highway in southeastern Ohio, a U.S. state. The southern terminus of SR 339 is at SR 618 approximately 2 miles (3.2 km) west of Belpre, and less than 0.50 miles (0.80 km) south of the U.S. Route 50 (US 50)/SR 7/SR 32 expressway. The highway's northern terminus is a T-intersection with SR 821 about 0.75 miles (1.21 km) south of Dexter City.

U.S. Route 50 runs east–west across the southern part of the state of Ohio, passing through Cincinnati, Chillicothe, and Athens. It is mainly a two-lane road except for the easternmost and westernmost parts. Near Athens it runs concurrently with State Route 32 (SR 32), a four-lane divided highway known as Corridor D, and from Coolville to the Ohio–West Virginia border it also overlaps SR 7 before crossing into Parkersburg, West Virginia.