State Route 550 (SR 550, OH 550) is an east–west state highway in the southeastern portion of the U.S. state of Ohio. The western terminus of State Route 550 is at an interchange with U.S. Route 33 just north of the city limits of Athens, immediately south of the southern terminus of State Route 13. The eastern terminus of State Route 550 is at an interchange with State Route 7 just west of Marietta.

Along its way, State Route 550 passes through the counties of Athens and Washington. There is no section of the highway that is incorporated within the National Highway System, a system of routes deemed most important for the country's economy, mobility and defense.

The debut of State Route 550 took place in 1976. This designation was applied to the route that was known as Alternate U.S. Route 50 up until that year, running between U.S. Route 33 just north of Athens and State Route 7 just west of Marietta. No major changes have taken place to the routing of State Route 550 since its inception. At least part of the route of 550 is based on the original Marietta-Chillicothe Stagecoach Road.