State Route 51 (SR 51) is a 114.183-mile-long (183.760 km) state highway in the southeastern and east-central parts of the U.S. state of Alabama. The southern terminus of the highway is at an intersection with U.S. Route 84 (US 84) near New Brockton. The northern terminus of the highway is at an interchange with I-85/US 29/US 280 at Opelika.