Abstract: In order to explore the effects of fermented feed on growth performance, antioxidant capacity and intestinal microorganisms of Macrobrachium nipponense, five experimental groups were designed as follow: L1 group (100% basal feed), L2 group (87.5% basal feed +12.5% fermented feed), L3 group (75% basal feed +25% fermented feed), L4 group (50% basal feed +50% fermented feed) and L5 group (100% fermented feed). M. nipponense of (0.09±0.01) g with similar size was selected for 56d culture experiment. The results showed that the contents of soluble protein and small peptide in the compound feed were significantly increased after feed fermentation (P<0.05), the number of beneficial bacteria was significantly increased, and the number of mold was inhibited after feed fermentation. The results of culture experiment showed that the survival rate of all groups was above 80%, and there was no significant difference (P>0.05). The weight gain rate was increased first and then decreased. The weight gain rate of L3 and L4 group was significantly higher than that of the control group (P<0.05), and the feed conversion ratio of L3 group was significantly lower than that of control group (P<0.05). The SOD activity of L3, L4 and L5 groups was significantly higher than that of L1 group (P<0.05), the MDA content of L2, L3 and L4 groups was significantly lower than that of L1 group (P<0.05), the superoxide anion clearance rate of L2 and L5 was significantly higher than L1 group (P<0.05), and the superoxide anion clearance rate of L4 group was significantly lower than that of L1 group (P<0.05). The contents of serum ALT, AST and ALB were significantly lower than that of control group (P<0.05), and the content of RUEA in L1 and L2 groups was significantly higher than that of other groups (P<0.05). GLU content in L2, L3 and L4 groups was significantly higher than that of L1 group (P<0.05). There were no significant differences in the contents of total triglyceride (TG), total cholesterol (TC) and total protein (TP) among all groups (P>0.05). The intestinal microbial results showed that the OTU number, Observed species index, Shannon index, and Chao1 index of group L3 were higher than that of group L1(P<0.05). PCA results showed that the community structure between group L1 and L3 was significantly different. At the genus level, the abundance of Aeromonas in group L1 was significantly higher than that in group L3 (P<0.05), and the abundance of Diverbacter and Bacillus in group L3 was significantly higher than that of group L1 (P<0.05). These results indicated that fermented diet could increase nutrient content, weight gain rate, reduce feed conversion ratio, improve antioxidant capacity and intestinal microbial community structure, and inhibit pathogenic bacteria in prawns. The suitable addition ratio of fermented feed is about 25%.