The seed of Japaness oyster, Crassostrea gigas(Thunberg), cultivated along the southerncoast of Korea have been transplanted and cultivated in both the Seonyu island and the Eocheong island of the western coast of Korea. The present study was carried out to investigate the growth of transplanted oysters, environmental factors influencing their fatness, and differences of two areas between the Seonyu island and the Eocheong island during the period from April to November, 1978. The results obtained were as follows: 1. Maximum height of the shell was 69.2mm (58.4mm on the average) in the island of Seonyu and 64.8mm(53.2mm) in the island of Eocheong, respectively. 2. The fatness of the oysters measured in the island of Seonyu (5.2g/month) was greater than in the island of Eocheong (2.5g/month) 3. The shell height was increased with high temperature while, the shell fatness with low temperature. 4. The growth rate of the transplanted seed oysters was twice as much as that of native ones in the western coast of Korea. 5. Environmental conditions of Seonyu island were more favorable in cultivating oysters than those of the Eocheong island.