The experiment was conducted to study the effects of sodium butyrate on growth performance and gut development in weanling piglets with or without infectious rotavirus inoculated, and to investigate the possible mechanism of sodium butyrate for relieving weanling stress. According to body weight, a total of 48 at (28±1)-day-old Large White weanling piglets were randomly allotted into 4 groups of 12 replicates and per replicate contained 1 piglet, which was fed in single cage. Using a 2×2 factorial design, control group and group 1 were fed with corn-soybean meal diet, group 2 and group 3 were fed with corn-soybean meal diet with addition of 0.3% sodium butyrate; group 1 and group 3 were inoculated with 1 mL (concentration: 1×106 TCID50/mL) rotavirus culture per pig at the experimental beginning. The experiment lasted for 21 days. The results were as follows: rotavirus significantly decreased ADFI and the ratio of jejunum villus height to crypt depth (P＜0.05 or P＜0.01), and significantly increased diarrhea index and jejunum crypt depth on day 14 after weanling (P＜0.05 or P＜0.01); rotavirus significantly elevated INF-γ (P＜0.05), IL-2 (P＜0.05), IL-6 level (P＜0.10) and rotavirus antibody express capacity (P＜0.01) on day 5 after weanling; sodium butyrate significantly increased ADG (P＜0.05) and ADFI (P＜0.01) on day 14 after weanling, and significantly decreased diarrhea index and jejunum crypt depth (P＜0.01), and significantly increased the ratio of jejunum villus height to crypt depth (P<0.01); sodium butyrate significantly improved Lactobacillui quantity in cecum (P＜0.01); sodium butyrate significantly elevated IL-4 level (P＜0.01) and rotavirus antibody express capacity (P＜0.05) on day 5 after weanling, and had a tendency to improve IL-2 and IL-6 level (P＞0.05). These results indicated that sodium butyrate could relieve stress induced by weanling and rotavirus inoculation, improve growth performance in weanling piglets. The mechanism could be that sodium butyrate improved intestinal tract development and microbial population structure, controlled cellular and humoral immunity to enhance the resistance to disease.［Chinese Journal of Animal Nutrition, ２００9，２1（5）:711-718］