Objective: To investigate the relations of Foxp3+ regulatory T cells (Tregs) with lymph node metastasis and proliferation of breast cancer. Methods: The CD4 (marker of regulatory T cells) and Foxp3 expressions in breast cancer tissues from 168 female patients were determined by immunohistochemical staining, using tissue specimens from 42 female patients with benign breast disease as control. The relations of Tregs with lymph node metastasis of breast cancer and the expression of nuclear proliferation-associated antigen Ki-67 were analyzed. Results: The numbers of both CD4+ T cells and Foxp3+ T cells (Tregs) in breast tissue was higher than those in breast tissue with benign disease, and both differences had statistical significance (both P<0.05); the numbers of both CD4+ T cells and Foxp3+ T cells in breast tissue with lymph node metastasis were higher than those in breast tissue without lymph node metastasis, but only the latter had statistical significance (P<0.05). The number of infiltrating Tregs showed no significant association with Ki-67 expression in breast cancer tissue (P>0.05). Conclusion: There is immunosuppression in microenvironment of breast cancer tissue, and the number of infiltrating Tregs is closely associated with lymph node metastasis, but irrelevant to tumor proliferation. It suggests that Tregs can be used as a new indicator for estimating presence or absence of lymph node metastasis in breast cancer patients.