The fish can reach an average size of 23 cm (9 in) in length. The body has an oval shape and is compressed laterally. Like other surgeonfishes, Acanthurus leucosternon swims with its pectoral fins. The caudal fin has a crescent shape. The fish has a “surgeon’s scalpel,” an erected part of the spine located at the base of the tail. The mouth is small and pointed in a beak-like manner with tiny and sharp teeth for reaching narrow spaces of food. Its sides are blue; its dorsal fin and the base of caudal fin are yellow; the head is black; the mouth, the throat area, the anal and pelvic fins are white. The pectoral fins are transparent with yellow reflections. The intensity of its blue color shows off if the fish is healthy or not. The fish does not undergo color changes as it matures; as some tangs, surgeonfish and unicornfish do.
