The effects of astragalus polysaccharide (APS) on nonspecific immune enzyme activities in plasma and the quantity of endocrine positive cells in stomach and foregut of tilapia were discussed in this paper. One hundred and fifty tilapia with body weight of (47±5) g were randomly divided into 5 groups with 3 replicates and 10 tilapia in each replicate. Four test groups were fed with experiment diets which constituted of basic diet supplemented with different levels of APS (500, 1 000, 1 500 and 2 000 mg/kg), while control group was only fed with basic diet. Tilapia blood was collected from the heart on the 10th day, 20th day and 30th day of the test and centrifuged to plasma. The activities of acid phosphatase (ACP), alkaline phosphatase (AKP), total superoxide dismutase (T-SOD), catalase (CAT), and lysozyme (LSZ) were measured. On the 40th day of the test, the quantity of proliferating cell nuclear antigen (PCNA) positive cells, inducible nitric oxide synthase (iNOS) positive cells and somatostatin (SS) positive cells in stomach and foregut was detected by immunohisto-chemistry antibody. Results showed that: compared with the control group, the activities of ACP, AKP, T-SOD, CAT and LSZ in 4 test groups were all increased, and 1 000 and 1 500 mg/kg groups were significantly or extremely significantly higher (P<0.05 or P<0.01) on the 20th day and 30th day. The results also showed that the quantity of PCNA positive cells in test groups was higher than that in control group, while the quantity of iNOS and SS positive cells was lower, and 1 000 and 1 500 mg/kg groups were significantly or extremely significantly different with control group (P<0.05 or P<0.01). In conclusion, the diet with APS could increase the ACP, AKP, T-SOD, CAT and LSZ activities and the quantity of PCNA positive cells, and decrease the quantity of iNOS and SS positive cells. The APS levels of 1 000 and 1 500 mg/kg had better effects.［Chinese Journal of Animal Nutrition, 2010，22（2）:401-409］