This experiment was used to study the effects of dietary Clostridium butyricum addition on growth performance, serum biochemical indices, immune function and disease resistance of grass carp （Ctenopharyngodon idellus）, in order to provide theoretical reference for application of C. butyricum in aquaculture. A total of 600 healthy grass carp with similar body mass of （23.78±0.68） g were randomly divided into 4 groups with 3 repeats for each group and 50 fish per repeat. Grass carp in the control group （T0 group） were fed a basal diet, while others in experimental groups （T1, T2, T3 groups） were fed basal diets added 1×10⁷, 1×10⁸, 1×10⁹ cfu/g C.butyricum, respectively. The experimental period lasted for 56 d. The results showed as follows： Dietary adding C. butyricum had significant effects on the weight gain rate （WGR） and specific growth rate （SGR） of grass carp, while had no important effect on survival rate （SR）. Conversely with the control group, the activities of superoxide dismutase （SOD） and lysozyme（LZM）, as well as the content of complement C3 were significantly higher in the experimental groups, while the activity of aspartate aminotransferase （AST） was significantly decreased. The expression of 4 immune-related genes （IL-8, IL-1β, IgM and TNF-α genes） in the experimental groups were significantly higher than that in the control group. After feeding probiotics for 56 days, the grass carp were challenged with Aeromonas hydrophila. The results indicated that the cumulative mortality rate of grass carp in the experimental groups were lower than the control group. Based on the results of this experiment, feeding basal diets added C. butyricum has a good impact on growth, immunity and disease resistance improvement for grass carp．