Objective: To investigate the alteration of CD4+CD25+Foxp3+ regulartory T cells (hereinafter abbreviated as Foxp3+ Tregs) in breast cancer patients and its significance. Methods: Forty patients with breast cancer and 32 patients with benign breast tumors were enrolled. The levels of Foxp3+ Tregs, CD8+CD28+ T cells and NK cells in peripheral blood of the patients were measured by flow cytometry, and the Foxp3 protein and mRNA expressions in breast lesions were determined by Western blot and RT-PCR, respectively. Results: The ratio of Foxp3+ Tregs was significantly higher, while the ratios of both CD8+CD28+ T cells and NK cells in peripheral blood were significantly lower in breast cancer patients than those in patients with benign breast tumor (all P<0.05), and there was a negative correlation between the level of Foxp3+ Tregs and either the level of CD8+CD28+ T cells or NK cells in peripheral blood of breast cancer patients (r=–0.631, r=–0.578, both P<0.05); the peripheral blood level of Foxp3+ Tregs in breast cancer patients was significantly decreased after operation compared with the level before operation (P<0.05). Either protein or mRNA level of Foxp3 in breast cancer tissue was significantly higher than that in benign breast tumor tissue (both P<0.05). Conclusion: Foxp3+ Treg and its molecular marker Foxp3 are increased in breast cancer patients, which may probably contribute to the tumor immunosuppression through inhibition of CD8+CD28+ T and NK cells.