South Carolina Highway 903 (SC 903) is a primary state highway in the U.S. state of South Carolina. It connects Lancaster to Darlington, Florence, and the Grand Strand.

SC 903 is a two-lane rural highway, from Catarrh to Lancaster. Control cities listed southbound include Myrtle Beach.

Established either in 1929 or 1930 as a new primary routing, it traversed from SC 35, in Catarrh, to SC 9, in Midway. In 1949, SC 903 was extended north to its current northern terminus in Lancaster, replacing an old alignment of SC 9.