The lipid class and fatty acid composition of prawns fed either a fat-free diet or those containing 5% each of oleic acid, medium chain triglyceride (MCT), pollack residual oil (PRO), and 1% each of linoleic, linolenic and docosahexaenoic acids supplemented by 4% of oleic acid or MCT were determined. The high contents of lipids, in which triglycerides were major class, were obtained from the better growth groups of PRO, and docosahexaenoic and linolenic additions. Although prawns are able to metabolize parent acids, such as linoleic and linolenic acids, to ω6 and ω3 highly polyunsaturated fatty acids (HPUFA) in the same way as demonstrated in fish, it is probable that their conversion ability is less active. Comparing the polar and nonpolar lipids of prawns, the former was characterized by the higher proportion of HPUFA than the latter.