The six species of Hydroporus Clairville recorded from Japan, Sakhalin and the Kuril Islands are revised. The following two syn. n. are established: Hydroporus watanabei Takizawa, 1933 = Hydroporus morio Aubé, 1838, and Hydroporus konoi Nakane, 1963 = Hydroporus submuticus Thomson, 1874. Hydroporus ijimai sp. n. is described from Hokkaido. The isolated position of Hydroporus tokui Satô, 1985, is noted, and the species is placed in its own species-group. An identification key is presented and species distributions are mapped.