Objective: To investigate the characteristics of breast cancer stem cells and their protein expression of RecQ family helicases.Methods: (1) Breast cancer stem cell were screened and cultured in serum-free medium.(2) CD44+CD24-/low were detected with flow cytometry for breast cancer stem cells.(3) The mRNA expression of drug resistant gene ABCG2 was detected with RT-PCR in breast cancer MDA-MB-435 stem cells and control cells.(4) The nude mice model of carcinoma was established to verify and compare the tumorigenicity of breast cancer stem cells with MDA-MB-435 cells.