Objective To study the changes of lymphocyte subsets and regulatory T cells in peripheral blood of patients with acute leukemia(AL) and its clinical significance.Methods The different levels of peripheral blood lymphocyte subsets and regulatory T cells of 60 AL patients and 40 normal controls were detected with flow cytometry.Results Compared with the normal controls,the percentages of CD3+ T cells,CD4+ T cells,CD16+CD56+ NK cells and the ratio of CD4+ /CD8+ obviously decreased in newly diagnosed AL group(P <0.05),while their percentages of CD8+ T cells and CD19+ B cells significantly increased(P <0.01).The percentage of CD4+ T cells and the ratio of CD4+ /CD8+ in acute lymphoblastic leukemia(ALL) group were much lower than those in acute myelogenous leukemia(AML) group(P <0.01).Compared with these in control group,the proportions of CD4+ CD25high Treg cells and CD4+ CD25+ T cells in newly diagnosed AL group were significantly increased(P <0.01).Conclusion Cellular immune function is significantly abnormal in patients with AL.Compared with AML patients,ALL patients had poorer cellular immune function.The increased CD4 + CD25high Treg cells might be one of the important reasons of immunosuppression in AL.Detection of lymphocyte subsets and regulatory T cells is of clinical value on the evaluation of therapeutic effect and prognosis in AL patients.