〔Abstract〕 To investigate the clinical characteristics and lymphocyte subsets of children with infectious mononucleosis complicated with multiple pathogens. One hundredchildren with IM were included and divided into simple EB virus infection group(53 cases) and multiple infection group(47 cases) according to pathogen infection. In addition,80 healthy children in the outpatient department of pediatrics were selected as the control group. The distribution characteristics of pathogens in the multiple infection group were analyzed. The clinical characteristics of simple EBV infection group and multiple infection group were compared,and the changes of lymphocyte subsets among three groups were compared. The main co-infected pathogens in children with IM were Mycoplasma pneumoniae(MP)(53. 19%) and Cytomegalovirus(CMV)(42. 55%). The incidence of pharyngitis,splenomegaly and liver function damage in the multiple infection group was significantly higher than that in the simple EBV infection group(P<0. 01). The expression levels of CD8+and CD3+in multiple infection group and simple EBV infection group were significantly higher than those in the control group(P<0. 01),while CD4+and CD4+/CD8+significantly decreased(P<0. 01). There were also differences between multiple infection group and simple EBV infection group(P<0. 01). The distribution characteristics of pathogens in children with IM were diverse,and the multiple infectious of EBV,MP and CMV were the main ones. Compared with simple EBV infection,the clinical symptoms of children with multiple infections were more serious,lymphocyte subsets were more disordered,and immune function was lower.