The total oil proportion of bay scallop by areas during the growing period was the highest (2.8%) at Tongyong in August, then it decreased to 1.88% in September and 0.62% in October, and it was the lowest (0.22%) in November. The total oil proportion of phytoplankton by areas was the highest at Tongyong, where it was decreased from 5.02% in August and 3.29% in September to 2.48% in October and 1.66% in November. For the composition of fatty acid of bay scallop by areas and seasons during the growing period, the major composition was 16:0 and 18:0 as saturated fatty acid, and 16:1n-7, 18:1n-7, 20:1n-9, ARA(20:4n-6), EPA (20:5n-3), DHA(22:6n-3) as monoenic acid. TMTD (4,8,12- trimethyltridecanoic acid) was detected in a little amount as special fatty acid. For the composition of fatty acid of prey by areas during the growing period of bay scallop from August to November 1998, n-3HUFA, Omega-3 highly unsaturated fatty acid, in August was 47.11% at Namhae in slowest growth, while it was distinctively low with 34.26% at Tongyong and 14.06% at Nammeon.