Ohio State Route 506 (OH 506) is an east–west state route in southern Ohio. Existing entirely in eastern Highland County, OH 506 has its western terminus at OH 124 in the hamlet of Marshall. Its eastern terminus is at OH 753 in another unincorporated community, Carmel.

OH 506 begins in the unincorporated community of Marshall at its junction with OH 124. The highway departs the hamlet heading eastward. It follows a reverse curve to the north, then takes on an east-northeasterly path into rural Marshall Township, dominated primarily by open fields. OH 506 intersects Blue Ribbon Road, then continues on to meet Turkey Road (Highland County Road 19). Passing by a few patches of trees amidst the open land, OH 506 next comes to back-to-back intersections with McCoppin Mill Road (County Road 51) and Slate Hill Road (County Road 77). Next, the state route experiences a series of smooth curves that turn it to the east, east-northeast, east again, and east-northeast yet again. At this point, as OH 506 has passed into Brush Creek Township, a pair of thicker patches of woods abut the north side of OH 506, which then re-enters fully into farmland. OH 506 next intersects Skeen Road, then curves to the northeast, and meets Carmel Road (County Road 76). Immediately after this intersection, OH 506 arrives at its junction with OH 753 in the hamlet of Carmel, where the highway comes to an end. The road that continues beyond OH 753 after OH 506 terminates is Cynthiana Road.

The OH 506 designation came into being in 1937, along the routing that it currently occupies. The only change that has occurred along OH 506 since its inception is the route that it intersects at its eastern terminus. As OH 124 has always been the highway serving as OH 506's western endpoint, the highway at its eastern end was first designated OH 70. Later on, that highway would be re-designated as OH 753.