This experiment was conducted to study the effects of magnesium ( Mg ) supplementation on growth, body composition and antioxidant ability of juvenile Chinese mitten crab ( Eriocheir sinensis) . Six ex-perimental diets were formulated with basal diet added of Mg ( the form of L-aspartic acid magnesium) of 0, 1.5, 3.0, 4.5, 6. 0 and 7. 5 g/kg, and the measured values of dietary Mg content were 0. 98, 1. 43, 3. 40, 4.79, 6.65 and 7. 98 g/kg, respectively. A total of 900 juvenile Chinese mitten crab with the average body weight of (2.97±0.01) g were randomly allocated to 6 groups with 5 replicates per group and 30 crab per rep-licate, and each group was randomly fed one of six experimental diets for 10 weeks. The results showed as fol-lows: the highest values of weight gain rate, survival ratio and crude protein content in whole-body were all found in the group with the Mg supplementation of 3.0 g/kg, but no significant differences in those indices a-mong all groups ( P>0.05) . There were also no significant differences in the daily feeding rate, feed conver-sion ratio, and the contents of moisture, crude lipid and ash in whole-body among all groups ( P>0.05) . The Mg content in whole-body was increased with the Mg supplementation increasing, while the highest value of calcium ( Ca) content in whole-body was appeared in the group without Mg supplementation, which lead to this group had the highest value of Ca/Mg in whole-body. The content of reduced glutathione ( GSH) in hepa-topancreas and serum was firstly increased and then decreased with the increase of dietary Mg supplementation, and the highest values were all found in the group with the Mg supplementation of 3.0 g/kg. The GSH content in hepatopancreas and serum in the group with the Mg supplementation of 3. 0 g/kg was significantly higher than that in the group with the Mg supplementation of 7.5 g/kg and the group without Mg supplementation, re-spectively (P<0.05). The content of malonaldehyde (MDA) in hepatopancreas and serum was firstly de-creased and then increased with the increase of dietary Mg supplementation, and the lowest values were found in the group with the Mg supplementation of 3. 0 g/kg, which was significantly lower than that in the other groups ( P<0.05) . In conclusion, the L-aspartic acid magnesium as Mg source, the juvenile Chinese mitten crab have the better growth effect when Mg supplementation is 3.0 g/kg;the GSH content in hepatopancreas as criterion, base on the quadratic regression model fitting, the juvenile Chinese mitten crab have the best antioxi-dant ability when Mg supplementation is 3.76 g/kg ( dietary Mg content is 4.39 g/kg) .