The Charleston Harbor is an inlet (8 sq mi/20.7 km²) of the Atlantic Ocean at Charleston, South Carolina. The inlet is formed by the junction of Ashley and Cooper rivers at . Morris and Moultrie Island. shelter the entrance. Charleston Harbor is part of the Intracoastal Waterway.

Like most river mouths in the Southeast, the inlet is evidence of a drowned coastline, created by a rise in sea level in recent geologic time.

The harbor froze over sufficiently to allow ice-skating during the winter of 1784, as a consequence of the volcanic outpouring at Laki in Iceland during the summmer of 1783.

See also: Waterways forming and crossings of the Atlantic Intracoastal Waterway