This study was designed to investigate the clinical significance of peripheral blood CD4(+) CD25(+) CD127 low-regulatory T (T(reg)) cells in acute myeloid leukemia (AML) patients. T(reg) cells in the peripheral blood of 80 AML patients and 35 age-matched healthy controls were counted by flow cytometry. Correlations between the frequency of circulating T(reg) cells and disease status, treatment outcome, or prognosis were evaluated. The percentages of T(reg) cells in patients at diagnosis and during refractory/relapse were significantly higher than that in healthy controls. There was no significant difference in the percentages of T(reg) cells between patients in remission and healthy controls. After six cycles of chemotherapy, the percentage of T(reg) cells in patients who achieved complete remission was significantly lower than that in patients at diagnosis, but there was no difference in T(reg) frequency between refractory/relapse patients and patients at diagnosis. T(reg) cells in the peripheral blood of AML patients may play a suppressive role in host antitumor immune response. The frequency of T(reg) cells in peripheral blood may thus be used as a biomarker for predicting sensitivity to chemotherapy and prognosis of AML patients. Additionally, T(reg) number in peripheral blood could be used to monitor disease status and evaluate disease progression.