Abstract: Objective To identify ALDH⁺ breast cancer stem cells in the human breast cancer tissues and investigate their proliferation and differentiation characteristics in vitro. Methods ALDH ⁺ breast cancer stem/progenitor cells isolated by the flow cytometry from human breast cancer tissue and stem cell biological characteristics were detected by culture ,colony formation assay, growth curve, and the transwell experimental methods. Results In breast cancer tissue, the total cell volume of ALDH⁺ of CD24^-/low CD44⁺ was 16%. After serum-free culture of 72 hours, a spherical-cell block gradually emerged and formed a spheroid at 2~3 weeks. ALDH⁺ stem cells of breast cancer had stronger invasive than ALDH^-breast cancer stem cells. Conclusion ALDH⁺ CD24^-/low CD44⁺ breast cancer stem cells existed in breast cancer tissue. ALDH might be used as a molecular marker to identify breast cancer stem cells.