An experiment was carried out in order to reveal the infection species of trematode and the infection demage in the marine bivalves. Metacercaria of Echinostomatidae were found in Mactra veneriformis, Cyclina sinensis and Solen strictus in the vicinity sea of Naecho-do, the estuary of the Keum River in the western coast of Korea. The metacercaria detected from Solen strictus were fed by Larus crassiostris, at 16 days after infection, the adult worm could be seceded. The metacercaria of Himasthla kusasigi were detected from Mactra veneriformis and Cyclina sinensis, their infection rates were 70.4% and 85.7% respectively. The partial infection rates with respect to the body parts were 40.4% and 77.3% in the foot, 17.0% and 12.4% in the gill, 12.6% and 10.3% in the mantle in order. The metacercaria of Acanthoparyphium were found from Solen strictus. The total infection rate was 63% and the partial infection rate was 63% and the partial infection rate was shown foot, mantle and gill in order. The adult worm ceded from Larus crassiostris was indentified as Acanthoparyphium tyosenensis Yamaguti, 1938 from view point of its physical characteristics. Therefore, Mactra veneriformis, Cyclina sinensis would be added as new intermediate hosts, and Echoinostoma decteded from Mactra sulcataria which was studied by author(1969) was revealed as larvae of Acanthoparyphium tyosenensis.