Objective To compare the changes of CD4+CD25+regulatory T cell in patients with idiopathic thrombocytopenic purpura(ITP) before and after treatment,and to analyze the effect of CD4+CD25+regulatory T cell in the pathogenesis of ITP.Methods Flow cytometry was used to test the CD4+CD25+regulatory T cell in peripheral blood of 40 ITP patients and 30 healthy people,and we investigated the change before and after treatment.Results The expression of CD4+CD25+regulatory T cell in patients with ITP before treatment was significantly lower than that of control one(P0.05),but it was higher than that of patients after treatment(except the ineffective group)(P0.05).The expression of CD4+CD25+regulatory T cell in patients with ITP after treatment was still lower than those of controls(P0.05).Compared to ineffective group,the levels of the CD4+CD25+regulatory T cell in effective group,moderate effect group and progress group were obviously higher(P0.05).However,there was no difference between moderate effect group and progress group(P0.05).Conclusion The expression of CD4+CD25+regulatory T cell in patients with ITP decreases,but it will increase after the treatment.So CD4+CD25+regulatory T cell may play an important role in ITP pathogenesis.