The composition of muscle lipids and their fatty acid composition of two groups of tilapia, cultured in fresh and seawaters, were investigated. The total lipid(TL) of seawater culture group is a little richer than that of freshwater culture. The neutral lipid(NL) is the most abundant in muscle lipids of two groups, followed by the phospholipid(PL) and glycolipid (GL). The increment of TL content seemed to depend upon triglyceride(TG) fraction, because large portions of lipids are consisted of TG. Phosphatidyl choline(PC), phosphatidyl ethanolamine and sphingomyelin were identified in PL, and the content of PC was the highest. The principal fatty acids of muscle lipids were 14 : 0, 16 : 0 and 18 : 0 as for saturated fatty acids, and 16 : 1, 18 : 1, 18 : 2 and 22 : 6 as for unsaturated fatty acids. In particular, high contents of 16 : 0 and 18 : 1 were observed in TL, NL and GL. However, low contents of 18 : 1 and 18 : 2 were observed in PL, while they were high in polyunsaturated fatty acids with 20 : 4, 20 : 5 and 22 : 6. In the meantime, no significant difference was observed in the composition of muscle lipids and their fatty acids between two groups cultured in seawater and freshwater.