Abstract: To study effect of fruc too ligosac charides on the ability of Non-specific immune function in Carassius auratus (initial body weight 50g), four experimental diets A1, A2, A3 and A4were formulated to contain 0.5g/kg, 1g/kg, 2g/kg and 4g/kg fruc too ligosac charides respectively, and the control (A0) contained no fruc too ligosac charides. The influence of fruc too ligosac charides was determined by examining their phagocytic activity of leukocytes, lysozyme activity, blood serum superoxide dismutase activity and the content of serum comp lement C3 in 7d, 14d, 21d, 28d, 42d and 56d, respectively. Theresults showed that the phagocytic activity of leukocytes, lysozyme activity, blood serum superoxide dismutase activity and the content of serum complement C3 in group A2 were significantly higher than the control group (p<0.05), which reached to the top level on the 28d, 21d, 14d, 14d, respectively. The phagocytic activity of leukocytes, lysozyme activity,blood serum superoxide dismutase activity and the content of serum comp lement C3 in group A were significantly higherthan the control group (p<0.05),which reached to the top level on the 14d, 14d, 7d, 14d, respectively. The content of srum comp lement C3 in group A3 was significantly higher than group A2 (p<0.05), there were no significant difference between group A3 and group A2 on the phagocytic activity of leukocytes, lysozyme activity, blood serum superoxide dismutase activity, but group A3 was higher than group A2. There were no significant difference between group A1, A4 and A0 on the phagocytic activity of leukocytes, lysozyme activity, blood serum superoxide dismutase activity, the content of serum comp lement C3 at other samp ling time.