The Chinese mitten crab,Eriocheir sinensis is an important freshwater aquaculture species in China.Molting death syndrome(MDS)is a common phenomena during the culture of E.sinensis,which maybe related to the deficiency and unbalance of lipid deposition in the body of E.sinensis.Therefore,this study was designed to investigate the dynamic changes of lipids in the hepatopancreas and muscle during the molting cycle of young E.sinensis by the biochemical analysis.Based on the changes of external morphology,the molting cycle of the crab was divided into four stages,premolt(D),molt(E),postmolt(AB),intermolt(C1 and C2).The results showed that there was significant difference on the total lipids of hepatopancreas among the different molting stages(P<0.05)and the trend of "high-low-high" was found for the total lipids in the hepatopancreas of E.sinensis.The opposite trend was found on the total lipids of muscle,and the trend was "low-high-low" with the highest total lipids in AB stage.The hepatopancreas had the high triacyglycerol(TG)levels while the muscle contained the high phospholipid(PL)percentages(% total lipids).The hepatopancreas TG decreased significantly from D to C1 stage,then increased significantly after that stage while the lowest TG level was found in the E stage of muscle.As for the fatty acid composition,the dominated fatty acids(≥4% total fatty acids)were C16:0,C18:1n9,C18:1n7,C18:2n6(LOA),C20:5n3(EPA)and C22:6n3(DHA)for both hepatopancreas and muscle.During the molting cycle,the saturated fatty acid(SFA)and polyunsaturated fatty acid(PUFA)remained relatively stable while the decreasing trends were found on monosaturated fatty acid(MUFA)and highly unsaturated fatty acids(HUFA)in hepatopancreas,and the highest DHA and EPA levels were found in D stage of hepatopancreas.For the muscle,the trend of "low- high-low" were found on SFA and MUFA while PUFA and HUFA had the opposite trends during the molting cycle of E.sinensis.In conclusion,the significant changes were found on the lipid classes and fatty acid composition for the hepatopancreas and muscle during the molting cycle,the hepatopancreas lipids may be one of the major energy source during the molting process of young E.sinensis.