Abstract: The study was conducted to examine the effect of dietary fatty acid composition on body composition and lip idetabolism of grass carp. Two semi-purified experimental dietswere formulated containing either triolein (Control diet) or fish oil concentrate rich in n-3 highly unsaturated fatty acid mixture (HUFA diet) as the main lip id source,and fed toup licate group s (-0 fish/tank) of grass carp (initial weight = 50 ±3 g/fish) for 4 weeks at 18-22℃. Fatty acid and roximate composition of different organs or body compartments,morphological characteristics,serum biochemical indica-ors,the activity of key enzymes of lip id metabolism,LPL mRNA expression,and hepatopancreas anti-oxidant systemsere determined at the end of the 4-week feeding trial. Dietary HUFA were incorporated into the fish body effectively.nalysis of fatty acid indicated that a higher content of C--: 6n-3 (P P PF),and a higher content of n-3 (P P P PF,and mus-le in fish fed the HUFA diet compared to the control diet. The content of IPF and hepatopancreas lip id (P P < 0. 05) was observed in the hepatopancreas of fish fed the HUFA diet. It could be concluded that theatty acid composition of the experimental fish was affected by fatty acid composition of the diet. However,the fatty acidomposition of different body compartments of grass carp differed significantly. Dietary HUFA might inhibit the activity ofipogenesis enzymes or decrease lip id storage leading to lower hepatopancreas lip id content. Dietary HUFA also had theositive effect on the antioxidant defense systems in grass carp.