This experiment was conducted to clarify the effects of fly maggot powder as a feed additive on the intestinal Escherichia coli count and the activities of antioxidant enzymes and digestion-related enzymes in serum of diarrhea mice. Seventy-five healthy male Kunming mice at 3 to 4 weeks of age were randomly divided into 5 groups with 3 replicates in each group and 5 mice per replicate. On days 1 to 5, the mice in the model group, 8.0%, 5.0% and 2.5% maggot powder groups were intraperitoneally injected with 0.02 mL/g of 3×10⁸ CFU/mL Escherichia coli suspension to establish a diarrhea model, the mice in the blank group was injected with an equal dose of sterile saline, and each group was fed a basic diet during the modeling period. On days 6 to 15, the mice in the 8.0%, 5.0% and 2.5% maggot powder groups were fed 2 g mixed diets with fly maggot powder additive dosages of 8.0%, 5.0% and 2.5%, respectively, and freely fed a basal diet after mixed diets. Model group and blank group mice freely fed the basal diet. The counts of Escherichia coli and total bacteria in the ileum, cecum and colon and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione S-transferase (GST), lactic dehydrogenase (LDH), amylase (AMS) and lipase (LPS) in serum of diarrhea mice were measured after the end of treatment period. The results showed that the count of Escherichia coli in the ileum, colon and cecum of the model group was significantly higher than that of the other groups (P<0.05). The count of Escherichia coli in the ileum, cecum and colon of the 8.0% fly maggot powder group was not significantly different from that of the blank group (P>0.05), but significantly lower than that of the model group and the 2.5% fly maggot powder group (P<0.05). The count of Escherichia coli in the colon of the 8.0% fly maggot powder group was lower than the blank group of 17.12×10⁴ CFU/mL. Diarrhea caused a significant decrease in the activities of antioxidant enzymes and digestion-related enzymes in serum of mice. After treatment 10 days, the activities of SOD, POD, CAT and GST in serum of the 8.0%, 5.0% and 2.5% fly mottle powder groups were significantly higher than those of the model group (P<0.05), and above four antioxidant enzyme activities in serum of mice increased with the increase of fly maggot powder additive dosage, while the serum GST activity of the 8.0% fly maggot powder group was significantly higher than that of the blank group (P<0.05). The activities of LPS, AMS and LDH in serum of the 8.0% and 5.0% fly maggot powder groups were significantly higher than those of the model group (P<0.05). The activities of LPS and LDH in serum of the 2.5% fly maggot powder group were also significantly higher than those of the model group (P<0.05). It can be seen that fly maggot powder can reduce the counts of Escherichia coli and total bacteria in the intestine of diarrhea mice, increase the activities of antioxidant enzymes and digestion-related enzymes in serum, and the fly maggot powder additive dosage of 8.0% has the best effect.