Objective To investigate the supplementary effect of intestinal tract microbial population moderator(Bifico) on chronic bronchitis.Methods Fifty patients of chronic bronchitis were randomly allocated into two groups,receiving either bifico or placebo respectively for six months.The change of incidence rates of respiratory tract infection,immunoglobulin(IgG,IgM,IgA) and CD4,CD8 were assessed before and after therapy.Results The incidence rates of respiratory tract infection declined from 25.0% to 4.1% in Bifico group,from 22.7% to 18.2% in the control group.There was a significant difference.In bifico,immunoglobulin IgA slightly decreased,IgG,IgM,C_3 slightly increased after treatment,IgG significantly increased((P<)(0.05)),C_3 appearently rised((P<)(0.05)).The rate of CD4/CD8 increased((P<)(0.05)),CD4 did not changed((P>)(0.05)),CD8 significantly declined((P<)(0.05))in bifico;there were no appearently changes in the control group before and after therapy.Conclusion Intestinal tract microbial population moderator has a role of immunoloregulation on chronic bronchitis,preventing its acute episde.