A taxonomic study of the Korean Hydrochus Leach is presented. They inhabit in the margins of shallow lentic water with plentiful vegetation. The genus Hydrochus Leach contains about 28 species in the Palaearctic region and only H. japonicus Sharp is recently listed in Korea. Here, two species are recognized, one of which is reported for the first time in Korea (H. chubu Balfour-Browne & Sato). This species are distinguished from H. aequalis Sharp by impressed pronotum and from H. japonicus by dark brown elytra. Habitus photographs, descriptions, and diagnostic characters with illustrations of the species are provided.