Gangesia parasiluri Yamaguti, 1934 (Cestoda: Proteocephalidae) is redescribed on the basis of adults obtained from the intestine of Silurus asotus Linnaeus (Teleostei: Siluridae) from Lake Suwa, Nagano Prefecture, central Japan. Its life cycle was studied in the field and laboratory. Rostellar hooks of the adults showed a wide variation in number, ranging from 35 to up to 57. Plerocercoids were found in the rectum of Chaenogobius urotaenia (Hilgendorf) and Rhinogobius brunneus (Temminck et Schlegel) (Teleostei: Gobiidae) from the same lake. Procercoids were formed in the haemocoel of Mesocyclops leuckarti (Claus) (Copepoda: Cyclopidae) 7 days post infection at 21-25°C. They developed into plerocercoids in the intestine of Pseudorasbora puntila pumila Miyadi (Teleostei: Cyprinidae), R. brunneus and S. asotus. Plerocercoids from naturally and experimentally infected fishes were fed to S. asotus, from which immature worms were recovered. It is considered that the life cycle involves three hosts: a copepod as the intermediate host in which procercoids are formed, small fish as paratenic hosts which retain plerocercoids and transport them into S. asotus, and S. asotus as the definitive host in which adults develop. Rostellar hooks of the adults were much fewer, much larger and arranged in fewer circles than those of the plerocercoids. It is suggested that the former are newly formed and replace the latter in an early stage of development of plerocercoids into adults in 5. asotus.