Specimens of Argulus japonicus Thiele, 1900 were collected from the body surface of the following cyprinids in Kagoshima Prefecture, Kyushu, western Japan: one and two live common carp (Cyptinus carpio) from a hobbist's pond and a reservoir in July 2007 and June 2012, respectively; a freshlydead koi carp (C. carpio) from a hobbist's pond in September 2011; and three freshly-dead Japanese crucian carp (Carassius cuvieri) from the Nakadake Dam Reservoir in June 2010. These collections represent the first records of A. japonicus from Kyushu Island. As many as 720 and more than 100 A. japonicus were found on the koi carp and each of the Japanese crucian carp, respectively. In the Nakadake Dam Reservoir, more than 1,000 Japanese crucian carp were found dead in early and mid-June 2010. It seems that the koi carp and the Japanese crucian carp were killed by the heavy infection of A. japonicus.