Specimens of Argulus japonicus Thiele, 1900 and A. coregoni Thorell, 1864 were collected in western Honshu, Japan. This is the first documented record of A. japonicus and the second record of A. coregoni from this region. Argulus japonicus was found to be parasitic on common carp (Cyprinus carpio) in Hyogo, Shimane and Yamaguchi prefectures and an unknown fish in Hyogo Prefecture. A swimming specimen of A. japonicus was taken in a river in Hyogo Prefecture. Argulus coregoni was sampled from river-resident and reared amago salmon (Oncorhynchus masou ishikawae) in Hiroshima and Hyogo prefectures, respectively.