Objective:To observe the efficacy of OM85-BV in the treatment of recurrent upper respiratory tract infection with adenoid hypertrophy and to explore its possible mechanism. Method:Four hundred and forty-eight children with recurrent upper respiratory tract infection and adenoid hypertrophy were collected. Three hundred and twenty-six patients in the control group were treated with conventional drugs, and one hundred and twenty-two patients in the observation group were treated with OM85-BV+conventional drugs, and the treatment lasted 12 weeks. The sleep obstructive symptoms of adenoid hypertrophy were scored according to OSA-18 before and after the treatment respectively(0, 6, 12 weeks). The symptoms scores and effective rate of treatment between the study and the control group were compared. The patients in the control group and the observation group who were unresponsive to drug treatment received surgery after 12 weeks of drug treatment. The levels of serum IL-2, IL-4, IL-6, IL-10, TNF, IFN-γ and IgE, the ratio of serum CD3, CD4, CD8 in lymphocytes and the ratio of CD4/CD8 were compared between the study and the control group before operation. The levels of HBD-2, IFN-γ, IL-4, IL-6 cytokines in the adenoid were compared between the control group and the observation group. The expression and distribution of adenoid HBD-2, IFN-γ, IL-4, IL-6 were compared between the control group and the observation group. Result:After 12 weeks of treatment, the total effective rate of the observation group was significantly higher than that of the control group, and the improvement of sleep respiratory obstruction symptoms of children with recurrent upper respiratory tract infection and adenoid hypertrophy was also much better than that of the control group. The serum IFN-γ of the observation group was significantly higher than that of the control group, and there was no significant difference in serum IL-2, IL-4, IL-6, IL-10, TNF, IgE between the observation group and the control group. There was no significant difference in serum CD3, CD4, CD8 and CD4/CD8 between the observation group and the control group. In the observation group, the adenoid HBD-2 was significantly higher but IL-4, IFN-γ were significantly lower than that in the control group, and IL-6 had no significant difference compared with the control group. Conclusion:OM85-BV can significantly improve the sleep apnea symptoms but can not rise the level of immune lymphocytes in children with adenoid hypertrophy and recurrent upper respiratory tract infection.OM85-BV can improve the Th1 immune response, enhancing the ability of human body to fight against pathogens and induce the release of HBD-2, increasing the resistance to microorganisms, reducing the bacteria aggregation, weakening the local inflammatory response in adenoids.