Abstract: Objective To investigate the infiltration of regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) in breast cancer and discuss its and significance. Methods From January 2017 to February 2018, 150 cases of breast cancer treated in our hospital were prospectively collected. Modified radical mastectomy was performed. Breast cancer specimens were taken during the operation. The expression of regulatory T cells and myelinated suppressor cells in breast cancer tissues were detected, and the correlation with the clinicopathological features was analyzed. Results There was no significant difference in the distribution of regulatory T cells and myeloid derived suppressor cells in breast cancer patients of different ages. The regulatory T cells of TNM stage for stage Ⅰ, stage Ⅱ and stage Ⅲ were 6.72±1.86, 9.61±2.45 and 12.05±2.81, respectively; and myeloid derived suppressor cells were 2.81±1.32, 4.92±1.92 and 6.01±2.65. With the increase of TNM stage, myeloid derived suppressor cells and regulatory T cells gradually increased (P<0.001). When compared with patients without lymph node metastasis, regulatory T cells and myeloid derived suppressor cells in patients with lymph node metastasis were significantly higher (P<0.001). The regulatory T cells of the patients with high differentiation, medium differentiation and low differentiation were 8.94±1.98, 9.83±2.05 and 10.99±2.42; and myeloid derived suppressor cells were 4.03±1.65, 4.87±1.91 and 6.22±1.89. All the differences were statistically significant (P<0.05). Pearson linear correlation analysis showed that myeloid derived suppressor cells and regulatory T cells were significantly positively correlated (r=0.271, P<0.001). Conclusion The expanses of regulatory T cells and myeloid derived suppressor cells in breast cancer is related to TNM staging, Lymph node metastasis and differentiation of tumor cells, and regulatory T cells and myeloid derived suppressor cells have synergistic effects.