This experiment was conducted to study the effects of Bacillus preparations on immunity and antioxidant activities in grass carp. A total of 315 grass carp, with similar initial weight (average weight of fish 45 g), were randomly divided into three groups with three replicates. The control group was fed the basal diet without Bacillus; treatment group 1 was added Bacillus preparation no. 1 with 1 × 10(8) cfu/m(3) per 7 days in culture water and also fed the basal diet; treatment group 2 was fed the basal diet mixed with 0.5 % Bacillus preparation no. 2, and the culture water was added 1 × 10(8) cfu/m(3) Bacillus preparation no. 1 per 7 days. After 4 weeks of culture, 12 grass carp from each replicate were taken randomly for the determination of immune response and oxidization resistance indices. The results showed that compared with control, the level of globulin and IgM of treatment group 2 was significantly increased (P < 0.05), which was also significantly higher (P < 0.05) than that of group 1. For the non-specific immunity index, compared with control, the lysozyme activity and complement (C3) content of treatment group 1 significantly increased (P < 0.05), and the level of myeloperoxidase and C3 of treatment group 2 was significantly higher (P < 0.05) than that of control, which was also significantly higher (P < 0.05) than that of group 1. In the serum, compared with the control, the level of total antioxidant activity (T-AOC), antisuperoxide anion free radical (ASAFR) and glutathione (GSH) of two treatment groups was significantly increased (P < 0.05); GSH content of treatment group 2 was significantly (P < 0.05) higher than that of treatment group 1 and control. There was no significant difference between T-AOC and ASAFR among the two treatment groups; no significant effect was found on glutathione peroxidase (GSH-Px) and maleic dialdehyde (MDA) among the three groups. In the liver, T-AOC, SOD, ASAFR, GSH-Px and GSH from two treatment groups were significantly higher (P < 0.05) than those of control; T-AOC, SOD and catalase from treatment group 2 were significantly higher (P < 0.05) than those of treatment group 1; and MDA of two treatment groups was significantly decreased (P < 0.05) as compared with the control. The results indicate that Bacillus preparations added into water can increase serum immunoglobulin levels and most of non-specific immune parameters content and enhance the antioxidant ability of grass carp, while adding Bacillus preparation into the water and feed is much better.