The present study was conducted to research some parastic trematodes species in marine bivalves which are widely distributed in the western sea in Korea. From April, 2001 to October, 2002, marsh calm (Corbicula japonica) were obtained from Kochang bay near the Sunun temple and razor calm (Sinonovaculla constricta) from Kaehwado. Short necked calm (Ruditapes philippnarum) were sampled from Ochungdo, Mardo and Kaeyado. Cercaria corbiculae was found in the gonad of C. japonica with a low infection rate of 0.83%. The cercaria and the sporocyst were sized 278×98㎛ and 890×275㎛, respectively. Some encysted larvae of Parvatrema duboisi sized 0.351×0.182mm were firstly found in the mantle of S. constricta in Korea. Each S. constricta contained 1-9 cysts and the infection rate was 48.3%. Cercaria tapidis was found in the both gonad and mantle of R. philippinarum. The annual average infection rate in the R. philippinarum from Ochungdo was 7.7%. This rate was much higher than those from Solri near the Kum river estuary in 1981. The infection rate of C. tapidis in R. philippinarum was different in sizes. The maximum rate was 4.8% in size 3.6-4.0㎝ and the minimum rate 0.8% in size 4-5㎝