Freshwater jellyfishes were collected from Taechong Dam reservoir in Korea on September 1994. Tiny nontentacled hydroids were also collected from Taechong Dam and Chuam Dam reservoirs in Korea between September 1995 to September 1997. The medusae were identified into Craspedacusta sowerbii Lankester, 1880 and tiny hydroids were found to be in its polyp stages. It belongs to the family 0lindiidae in Limnomedusae and is first recorded from Korea. Environmental factors affecting the medusa occurrence are discussed.