Abstract: One hundred and twenty tilapia were randomly divided into 5 groups in this experiment.Four test groups were fed with basic diet with different levels of astragalus polysaccharides (100, 500, 1 000, 1 500 mg穔g-1), while control group was only fed with basic diet for 40 days.The leukocyte phagocytosis activity and the weight of immune organs of tilapia were detected respectively every ten days.The result showed that group 500 mg穔g-1,1 000 mg穔g-1 and 1 500 mg穔g-1 were significantly different with the control group on phagocytosis activity and the growth of immune organs (P-1 did not have significantly different with the control group (P>0.05).It indicated that astragalus polysaccharides could enhance phagocytosis activity and the growth and maturity of immune organs.