Abstract: Objective To investigate the effects of acidic tumor microenvironment on maintaining stemness and underneath mechanism in breast cancer stem cells. Methods Cultured the human breast cancer cell MDA-MB-231 with either pH 6.8 or pH 7.4 medium, the percentage of ALDHhigh subpopulation, the expression of SOX2, OCT4, Lin28b and the stemness properties were detected by using FCM, Real-time PCR, Western blot, sphere test and scratch experiments. The activation of signaling pathway was also detected. Results All stemness properties of MDA-MB-231 cell cultured with pH 6.8 conditional medium were increased including the percentage of ALDHhigh subpopulation（P<0.05）, the expression of stemness gene（P<0.01）, the capability of sphere formation（P<0.01） and cell mobility（P<0.05）. These stemness properties of MDA-MB-231 cell were regulated via β-catenin/TCF4 signaling pathway that activated by pH 6.8 cultured medium. Conclusion The acidic tumor microenvironment increases the percentage of ALDHhigh subpopulation and enhances stemness phenotypes of breast cancer cells.

Key words: breast cancer, cancer stem cells, acidic microenvironment.