Abstract: Objective To study the influence of secreting type antibacterial peptides from Musca domestica larvae on the immune system of normal mice.Methods Thirty-two BALB/c mice were selected and divided randomly into four groups.Different doses of secreting type antibacterial peptides(5,10,20 mg/kg)were administered to the mice with intraperitoneal injection for 7 days.A series of classical tests were adopted to evaluate the effects.Results In the 10 mg/kg and 20mg/kg dose groups,the ratio of spleen/body weight were 7.41±0.93 and 7.56±1.05;the phagocytotic ability of macrophages were 38.81±7.88 and 40.16±9.74;the lymphocyte transformation induced by conA of the mice were 0.31±0.11 and 0.32±0.09.All the indexes were higher than those of the control with statistically significant differences(P<0.05 for all).But the body weight and the 50 percent hemolyzingdose of complement of the 5-20mg/kg dose groups were not different from that of the control group.Conclusion The secreting type antibacterial peptides from Musca domestica larvae could promote the immune function in normal mice.