The freshwater goby, Rhinogobius sp. TO, is endemic to Japan and occurs only in the Tokai District, central Honshu, Japan. The lernaeid copepod, Lernaea cyprinacea Linnaeus, 1758, and the argulid branchiuran, Argulus sp., were collected from specimens of this goby in Aichi Prefecture. These crustaceans are the first parasites found from Rhinogobius sp. TO.