A harpacticoid copepod, Sinamphiascus dominatus Mu & Gee, 2000 is re-described from the sandy bottom in off Jeju Island of Korea. The genus Sinamphiascus was established with single species, S. dominatus from the Bohai Sea, China. The main diagnostic characters of the specimen from Korea are well matched with the original description, although it has minor discrepancies including the lengths and ornamentation of setae in leg 6 of both sexes, shape of the base on furcal setae and teeth number of labrum in female. However those discrepancies are regarded to the intra-specific variations. This is the first record of genus Sinamphiascus in Korean waters.