Abstract: To investigate effects of Achyranthes bidentata polysaccharide (ABP) on immunity and antioxidant function of grass carps, five test groups were used, which consisted of control group, 0.05%, 0.10 %, 0.20 % and 0.40 % ABP addition group. 375 grass carps with similar body weight (88.130.76) g were randomly allotted to five groups with three replicates and with 25 grass carps in each replicate and were fed for 65d. The results showed as follows: compared with the control group, 0.20% ABP addition significantly increased the contents of serum tumor necrosis factor- (TNF-), the activities of serum superoxide dismutase (SOD), acid phosphatase (ACP) and lysozyme (LZM) (P0.05), significantly decreased the contents of serum malondialdehyde (P0.05). 0.40% ABP addition significantly increased the contents of serum total protein (TP) and the activities of serum alkaline phosphatase (AKP). 0.10% ABP addition significantly increased spleen somatic index of grass carp. However, the number of Nitroblue tetrazolium (NBT) positive cells, the contents of serum albumin (ALB), interleukin 1(IL-1) and interleukin 6 (IL-6) were not significantly affected by ABP supplementation (P0.05). These results indicate that dietary appropriate ABP can significantly promote immunity and antioxidant function of grass carps. We suggest that the appropriate ABP content was 0.20 % in feed of grass carp.