Abstract: In this paper,the antibacterial effect of chitosan on infection was reported.The Kun-ming mice receiving on intraperitoneal injection of chitosan in the dosage of 300mg per kilo-gram body weight for three times were then infected in the abdominal cavity by staphylococ-cus aureus or E.coli.The condition of health of mice was observed.It was found that the weight and number of death of the mice pretreated with chitosan were significantly different from that of control group(P<0.05).Chitosan in vitro has no direct bactericidal effect.It is indicated that chitosan has the antibacterial effect by immunomodulation.

Key words: chitosan, chitin, immunomodulation