A species of freshwater sculpin, Japanese name "Kibire-kajika", inhabits some rivers of the Korean Peninsula. Although this species has been recorded under the name Cottus poecilopus Heckel, 1840 or the incorrect subsequent spelling C. poecilopterus, it is shown by comparison with the type specimens to differ from both subspecies of C. poecilopus (C.p. poecilopus Heckel, 1840 and C.p. volki Taranetz, 1933). Moreover, it is distinguished from all other members of the genus Cottus by the following combination of characters: lacking palatine teeth, pectoral fin rays not branched even in adults, lateral line complete, terminal pores of mandibular sensory canals opening separately on either side of symphysis, body almost naked, back and sides lacking dark vermiculations, pelvic fin with bands or white roundish marks bordered with a blackish line, innermost ray of pelvic fin longer than 60% of length of longest ray, second dorsal fin rays numbering 18-21, anal fin rays 14-17, pectoral fin rays 12-13, and vertebral number 34-36. We describe this species here as a new species, Cottus koreanus, on the basis of 28 specimens collected from several rivers in Korea.