In order to study the relationship between the ultrastructure,lipid profile of gills and their different habitats,the gills of three typical crabs living in different habitats were chosen as experimental materials.They are Portunus trituberculatus,Sesarma dehaani andEriocheir sinensis,living in the seawater,estuary(or near freshwater)and freshwater respectively.The ultrastructure and lipid profile were also compared by using electron microscope and biochemistry,aimed to provide the basic data for comparative physiology and biochemistry in crustacean,and promote the understanding of the physiological functions of the ultrastructure and lipid profile in gills.The results indicated that the ultrastructure of gill filaments in the different crabs were similar,with cuticle,epithelial cell and a central haemolymph space,but the amount of mitochondrion and the microvilli in the three kinds of crabs had significant difference:the density of mitochondria in the anterior gills of the Chinese mitten crab was significantly higher than the other two crabs(P＜0.05),and in posterior gills of P.trituberculatus was significantly lower(P＜0.05).Besides,P.trituberculatus has lower density of microvilli,compared to the other two crabs.The content of triglyceride(TG)in the anterior of P.trituberculatus was higher than that in the others(more than 3 times,P＜0.05),also the content of cholesterol(Cho)in the gills of S.dehaani was significantly higher than the other two crabs(P＜0.05),while the contents of the phospholipids showed no significant differences between the three kinds of crabs(P＞0.05).The gills of S.dehaani have a significantly higher arachidonic acid(ARA)and total highly unsaturated fatty acids(HUFA)content than that of E.sinensis and P.trituberculatus(P＜0.05).The result shows that the significant differences in the ultrastructure,contents of total lipids and fatty acids contributed to their normal physiological function and their adaptation to their habitats.