Objective: This study investigated miR-422a and PLP2 expressions in breast cancer cells and breast cancer stem cells (BCSCs). Besides, their influences on polymorphism changes were observed.Methods: Flow cytometry and fluorescence-activated cell sorting was performed and CD24(-)/CD44(+) cells were sorted from breast cancer cells and recognized as BCSCs. Microarray was applied to search for the differentially expressed miRNAs and mRNAs between MCF7 and BCSCs. The aberrant expression of miR-422a and PLP2 was further confirmed by RT-qPCR and the direct targeted relationship was verified by dual-luciferase reporter assay. After in vitro transfection, the expression of miR-422a and PLP2 were manipulated and biological functions of BMSCs were compared with CCK-8, colony formation and sphere formation assay. The tumorigenesis ability of transfected BMSCs was also investigated in NOD/SCID tumor mice models.Results: BMSCs were successfully established from MCF7 cells and miR-422a expression was downregulated while PLP2 level decreased in BMSCs. MiR-422a directly targets the 3UTR of PLP2 and suppressed its expression. Besides, the up-regulation of miR-422a contributed to weakened ability of proliferation and microsphere formation of BMSCs, while PLP2 overexpression facilitated those biological abilities. Tumorigenesis of BMSCs in mice models was impaired by either overexpression of miR-442a or silencing of PLP2.Conclusion: Up-regulation of miR-422a attenuated microsphere formation, proliferation and tumor formation of breast cancer stem cells via suppressing the PLP2 expression.