Abstract: From December,2000 to October,2001,100 fishes of Mystus macropterus were collected in Winter,Spring,spawing period,spent period and Autumn in the Jialing River.Of which there were 10 males and 10 females respectively in a sample during each season.The energy density and composition of the fish body were measured.The result showed that there was no significant difference of either body composition or energy density between males and females in each season.In the female,the protein content(16.23%),energy density(6.14kJ/g),lipid content(5.84%),and dry mass content(26.67%)in the Autumn were significant higher than those in any other samples.In the Winter,the female has the lowest lipid content(2.39%)and the energy density(4.55 kJ/g).In the male,the highest energy density(5.85kJ/g)and protein content(16.34%)appeared in Autumn,and the lowest 1ipid content(1.31%),energy density(4.16kJ/g),dry mass content(22.49%)appeared in the Spring.There was significantly linear relationship in each sample between energy density and either dry mass or lipid content,respectively.By analysis of covariance(ANCOVA)on the regression equations of energy density(E:kJ/g)to dry mass(D:%B.W.)in the 10 samples,four equations were developed as the predicting models for the different samples.The first model is for the female samples in Winter,Spring,post-spawing and Autumn i.e.non-spawing seasons:E=-5.573+0.437D;the second one for the females in spawing period:E=-0.605+0.250D;the third one is for the male samples in Winter, Spring,post-spawing and Autumn i.e.non-spawing seasons:E=-6.046+0.456D,and the fourth one for the male sample in spawing period:E=-3.64+0.366D.