Objective To explore the inhibition effects of CD4+CD25+/highCD127low on the EBV immortalized cells(CD23+)in children with infectious mononucleosis (IM). Methods The expression of CD3+, CD3+ CD4+ , CD3+ CD8+ , CD25+/highCD127low and CD19+ , CD19+ CD23+ were analyzed by flow cytometry in 23 children at the acute stage of IM and 10 children recovering from IM in comparison with the ones of 20 healthy controls. Results Compared with the following results in controls, CD3+, CD3+ CD8+ were significantly increased and CD3+ CD4+, CD4+/CD8+ ratio, CD4+ CD25+/highCD127low, CD19+, CD19+ CD23+ were significantly reduced in the IM patients. Compared with the ones in the IM pa-tients recovering from IM, CD3+ , CD3+ CD8+ were significantly increased and CD3+ CD4+, CD4+/CD8+ ratio, CD4+ CD25+/highCD127low, CD19+ , CD19+ CD23+ were significantly reduced in the IM patients at the acute stage. There was no obvious difference in all the marks except CD4+/CD8+ratio, CD8+ CD28+ , CD19+ , CD19+ CD23+ ratio between the children recovering from IM and the normal controls. There is a positive correlation between CD3+ and CD19+, CD19+ CD23+ during acute phase. There is a negative correlation between CD4+ CD25+/highCD127low and CD19+ , CD19+ CD23+ during acute phase. Conclusion The results indicate that the decreasing of CD4+ CD25+/highCD127low may play an important role in elimina-ting EBV immortalized cells.