Abstract: Different body-size young Chinese mitten crabs (Eriocheir sinensis), living from the end of the last winter to the beginning of the first molting in the second year, were fed with three different diets, the corn, the crusion carp meat, and the formulated diet. And the energy density of the whole crab, the content of total lipid and crude protein in the hepatopancreas and muscle were dentermined. The result showed that, the energy density of the whole crab rised firstly, and then declined to the same level with that before feeding. The energy density early in the feeding of formulated diet group was significantly higher than that of the other groups (P<0.05). The energy density of big body-size crabs was higher than that of small body-size, but the difference was not significant (P>0.05). And the energy density of the big body-size crab in the group fed with corn was significantly higher than that of the others (P<0.05). The content of total lipid and crude protein in the hepatopancreas in all groups showed no significant differences (P>0.05). The content of both total lipid and crude protein in the muscle of small body-size crabs declined significantly (P<0.05), while the total lipid of big body-size crabs showed no significant differences (P>0.05), but the content of crude protein rised significantly (P<0.05).