Based on a single specimen (49.9 mm SL) collected from Incheon River estuary, south-western Korea, Gymnogobius cylindricus was described as the first record from Korea as well as the westernmost record of the world. The species is characterized by having a large maxilla extend far beyond posterior margin of eye, dorsal fin with VI-I, 12 rays, anal fin with I, 11 rays, and without dark blotches and dots on lower part of body and caudal fin, respectively. A new Korean name, "Ga-neunsal-mang-dug" is proposed for the species.