The effects of chitosan on growth performance, fecal score, serum hormones and T lymphocyte subset of weaned piglets were investigated in this study. A total of 60 weaned piglets (weaned at 28 days of age) were selected and randomly assigned to 5 groups, and each group contained 12 piglets. Piglets in control group were fed a basal diet, and those in experimental groups were fed the basal diet supplemented with 250, 500, 1 000 and 2 000 mg/kg chitosan, respectively. The experiment lasted for 14 days. The results showed as follows: 1) diet supplemented with 250 to 2 000 mg/kg chitosan significantly increased average daily gain (ADG) (P<0.05), and significantly decreased feed/gain (F/G) of weaned piglets (P<0.05). 2) Diet supplemented with 250 to 2 000 mg/kg chitosan significantly decreased fecal score on the day 11 of weaned piglets (P<0.05). 3) Diet supplemented with appropriate dose of chitosan significantly increased serum concentrations of growth hormone-releasing hormone (GHRH) (250 to 2 000 mg/kg), growth hormone (GH) (500 to 1 000 mg/kg) and leptin (LP) (2 000 mg/kg) (P<0.05), and significantly decreased serum concentrations of corticotropin releasing hormone (CRH) (250 to 2 000 mg/kg), adrenocorticotropic hormone (ACTH) (500 to 1 000 mg/kg), cortisone (COR) (250 to 2 000 mg/kg)and soluble CD8 (sCD8)(500 to 2 000 mg/kg) of weaned piglets (P<0.05). The results suggest that diet supplemented with appropriate dose of chitosan can improve the growth, reduce the diarrhea and alleviate the weaning stress of weaned piglets.