This experiment was conducted to discuss the effects of astragalus polysaccharide on the structure of intestinal villus and distribution and quantity of intestinal mucous cells and intraepithelial lymphocytes of tilapia. One hundred and fifty tilapia with average body weight of 47 g were randomly divided into 5 groups with 3 replicates each and 10 fish in each replicate. Five groups were fed basal diet supplemented with 0, 500, 1 000, 1 500 and 2 000 mg/kg astragalus polysaccharide,respectively. After 40 days, 5 tilapia in per group were randomly selected, anatomized, taken out intestine, fixed, embedded and sliced. Then the structure of intestinal villus and the distribution and quantity of mucous cells and intraepithelial lymphocytes were observed by histochemical staining method. Results were as follows: the structure of intestinal villus in all groups were rather integrally. The length of intestinal villus, depth of crypt, thickness of muscular and quantity of intestinal mucous cells and intraepithelial lymphocytes in four experimental groups were larger than those in control group, and that in 1 000 and 1 500 mg/kg groups had significantly improved except thickness of muscular and quantity of intraepithelial lymphocytes in foregut（P<0.05 or P<0.01）. In conclusion, supplementing astragalus polysaccharide to the diet could improve the length of intestinal villus, depth of crypt, thickness of muscular and quantity of intestinal mucous cells and intraepithelial lymphocytes of tilapia, and the appropriate addition levels were 1 000 and 1 500 mg/kg.［Chinese Journal of Animal Nutrition, 2010，22（1）:108-116］