The development of Echinestcma cinetorchis in several snail species reared in laboratory aquaria was observed. The eggs from adult cukes collected from the intestine of rats were cultivated to miracidia, and exposed to Hippeutis sp. snails. Observations were made for cercarial shedding from the exposed snails. The cercariae shed from the snails were again exposed to several species of fresh water snails in order to observe metacercarial formation in the snails and their infectivity to final hosts. The results obtained in this study were as follows: 1. Twenty miracidia were exposed to each snail of Hippeutis sp. About 58.3% of the above snails (7 out of 12) were dead before shedding the cercariae, anti the remainder shed the cercariae for a period of 7 to 9 days before death. 2. Cercarial shedding from the infected snails started from the 25th day after the exposure to mi.acidia, and the total number of cercariae shed per snail was 684 in average (range; 482-904). 3. The sixte of refine developed in the infected Hippeutis sp. snails was 1$, 242{ imes}214{;}{mu}m$ in average, and the number of rediae per snail was 350 in average (range; 120-510). 4. About 40 to 50 cercariae shed from the Hippeutis sp. snails were each exposed to several species of snails reared in the laboratory. The metacercarial formation was confirmed by dissecting the infected snails, 12 to 16 days after the infection. The infectivity to each snail species was 100% in Hippeutis sp. (recovery rate; 56.7%) and Radix auricuzaria coreana (recovery rate; 66.4%), 66.7% in Physa acute (recovery rate; 37.5%), and 50% in Cipangopaludina sp. (recovery rate; 8.0%), respectively. 5. The swimming cercariae attached first at the cephalo-podial part of the snails and then migrated to the mantle, internal organ s and hemocele areas to form the metacercariae. 6. Adult worms of E. cinetorchis were obtained from the rats infected with the metacercariae encysted in the experimental snails. Summarising the above results, it is suggested that the mud-snail (Cipangopaludina sp.) may play an important role as a source of human infection with E. cinetorchis in Korea, and that several species of fresh water snails are involved in the life cycle as a second intermediate host.