Total fatty acid compositions of wild and cultured yellowtails were examined. 1) The major fatty acids in several tissues of wild and cultured yellowtails were examined and found to be C16:0, C18:1 (n-9), C20:5 (n-3), and C22:6 (n-3). In the same fish, similar fatty acid profiles were found in the dorsum, abdomen, dark tissue, and skin. But the profile in liver differed from these due to the possibly higher level of C18:1 (n-9) and lower level of C22:6 (n-3). 2) In yellowtails caught in March and November, no differences were observed in the fatty acid profiles in hard and soft roes of muscle tissue. However, fish caught in May had lower levels of C14:0, C16:1 (n-7) and C18:1 (n-9), and higher levels of C16:0 and C22:6 (n-3) in the soft roe, and lower levels of C14:0 and C16:0 and higher levels of C18:1 (n-9) and C22:6 (n-3) in the hard roe than those caught in March and November. 3) In wild yellowtails, hardly any difference could be found in the fatty acid profile in adult specimens (body length : about 67cm), but were remarkable differences in the levels of C16:0 and C18 :1 (n-9) in young fish (body length : about 30cm). The fatty acid profile of an adult fish differed from that of a young fish. 4) The fatty acid profiles of cultured yellowtails could be classified in two groups on the basis of C18:1 (n-9) and C20:5 (n-3) levels. However, no causal relation appeared to exist for the differences between fish size and rearing form or the season in the fish were caught.