The hepatopancreas index ( HI) , lipid content ( LC) and fatty acid composition in Eriocheir sinensis before and after the precocity, were compared by gravimetry and gas chromatography. The results showed that HI and lipid content both decreased after the precocious molt, regardless of their sex. As for fatty acid composition of hepatopancreas, immature male and female individuals were very similar, except for C20..5n- 3 significantly higher in the latter ( P < 0. 05) . However, it varied with the sex when the precocious and immature crabs were compared. In female, the percentage content of C16..1n- 7, C16..0 and C18..0 were signif icantly higher in precocious individuals, but that of C20..4n- 6, C20..5n- 3( EPA) and C22..6n- 3( DHA) signif icant ly lower( P < 0. 01) . And in male, there was only C18..1 signif icant ly higher ( P < 0. 05) in precocious individuals while C14..0 ( P < 0. 05) , C16..1n- 7( P < 0. 05) and C20..5n- 3( P< 0. 01) lower. According to the results, it might come to the conclusions that EPA is very important during precocious molt and construction of membranes, while DHA mainly participates in the development of ovary and vitellogenesis.