Objective To explore effect of immune function of children with EB virus infectious mononu-cleosis (IM). Methods From Sep. 2011 to Jun. 2013, a total of 62 cases of children with IM were analyzed retrospectively. The proportion of T-lymphocyte subsets ,B-lymphocytesand and NK cells in EBV-DNA group with positive and negative were compared. Results The numbers of IM EBV-DNA-negative cases were 18 (29.03%), the numbers of IM EBV-DNA-positive cases were 44(70.97%), the averages of EBV-DNA in positive group is 6.1 × 103/mL. CD3+,CD8+cell ratios in IM children are significantly higher than control group (P<0.01), CD4+, CD19+cell ratios are significantly lower than control group (P<0.01), NK cells are not significantly different (P>0.05). In the IM children, CD4+, CD19+cells in DNA-positive group are significantly less than DNA-negative group (P<0.01), CD8+cells are higher than DNA-negative group (P<0.05), NK cells are not significantly different (P>0.05). Conclusions Positive blood EBV-DNA is closely related to changes in T-lymphocyte and B-lymphocyte, but isn′t obviously related in NK cells. So effect of EB virus in IM child have certain clinical values to judge the severity and prognosis.