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.