Objective: To investigate the value of determination of the peripheral blood level of CD4+CD25+Foxp3+ regulatory T cells (Treg) in breast cancer patients. Methods: The percentage of CD4+CD25+Foxp3+Treg cells in CD4+ T cells in the peripheral blood from 74 breast cancer patients and 30 healthy controls were measured by flow cytometry. The relations of CD4+CD25+Foxp3+Treg cell level with the clinicopathologic factors and relevant immunohistochemical parameters of the breast cancer patients were analyzed. Results: The percentage of CD4+CD25+Foxp3+Treg cells in CD4+ T cells of breast cancer patients was higher than that of healthy controls [(9.15±2.24)% vs. (2.29%±1.36%)], and the difference had statistical significance (P<0.05). Statistical analyses showed that the peripheral blood level of CD4+CD25+Foxp3+Treg cells of breast cancer patients was significantly related to histological grade, lymph node metastasis, pTNM stage and expressions of HER-2, pS2 and nm23 (r=0.583, r=0.333, r=0.919, r=0.604, all P<0.05), and irrelevant to tumor size, pathological type and the expressions of estrogen receptor (ER), progesterone receptor (PR), p53 and Ki-67 (all P>0.05). Further correlation analyses demonstrated that CD4+CD25+Foxp3+Treg cell level was positively correlated with histological grade, number of lymph node metastasis, pTNM stage and Her-2 expression and negatively correlated with pS2 and nm23 expression (r=–0.229, r=-0.401, all P<0.05). Conclusion: The peripheral blood level of CD4+CD25+Foxp3+Treg cells is increased in breast cancer patients, which also is closely related to the progression and metastasis of breast cancer. So its determination may offer certain implications for evaluation of the prognosis and therapeutic effects of the patients.