Abstract: Forkhead Box Protein 3 (FOXP3) is a transcription factor critically involved in the development and functions of immunosuppressive CD4+CD25+ regulatory T cell (Treg). FOXP3 expression was thought to be restricted to Treg, however, recent studies have provided clear evidence that various types of human tumor cells expressed FOXP3, including breast caner. But the subcellular localization and the extent to which FOXP3 is expressed in human breast cancer epithelial cells are conflicting. Many preclinical studies have demonstrated that FOXP3 acts as an X-linked tumor suppressor gene in the pathogenesis of breast cancer, while, more clinical studies reported unfavorable prognosis of tumors with FOXP3 expression. Despite increasing knowledge about the biology of FOXP3 in breast cancer cells, the biological functions and significance of FOXP3 expression in breast cancer remain still controversial and not clearly defined. Here, the present review discusses the role of FOXP3 in breast cancer aiming at new strategies for breast cancer prognosis.