Abstract: Objective: To explore the relationship between the level of CD4+＞ CD25+＞ T cells and pathogenesis or prognosis of aplastic anemia by detecting CD4+＞ CD25+＞ T cells in peripheral blood.Methods: The proportion of CD4+＞ CD25+＞ T cells and CD4+＞CD25high＞ T cells in peripheral blood of four groups, including 20 cases of healthy individuals as normal controls, 30 cases of patients with first onset of aplastic anemia, 10 cases of patients accepted effective treatment and 10 cases of patients accepted invalid treatment,were determined by flow cytometry.Results: The rate of CD4+＞ CD25+＞ T cells in peripheral blood of four groups was not significantly different(P ＞0.05); Compared with group of normal controls, the rate of CD4+＞ CD25high T cells in patients with first onset of aplastic anemia decreased significantly(P＜0.01-P＜0.05),but did not when compared with patients accepted effective treatment(P ＞ 0.05).Conclusions: The decreasing of CD4+＞ CD25highT cells is one of the reasons causing breakdown of immune tolerance in patients with aplastic anemia, the rate of CD4+＞ CD25+＞ T cells may not reflect the prognosis of the patients.