Objective To investigate the expression of miRNA-101 and its effect on the proliferation ability in breast cancer MDA-MB-231 cells. Methods qRT -PCR was used to detect the expression of miRNA-101 in breast cancer MDA-MB-231 cells and normal mammary epithelial MCF-10A cells. miRNA-101-mimic/inhibitor/NC were transfected into MDA-MB-231 cells by Lipofectamine TM 2000. qRT-PCR was used to detect the transfection efficiency. CCK-8 assay was used to evaluate the proliferation ability of MDAMB-231 cells after the transfection. Results The expression of miRNA-101 in MDA-MB-231 cells was significantly lower than that in MCF-10a cells (p < 0.05). The proliferation ability of MDA-MB-231 cells was significantly decreased after transfection with miRNA-101 mimic (p < 0.05), while the proliferation ability was significantly increased after transfection with miRNA-101 inhibitor ( < 0.05). Conclusions miRNA-101 is down-regulated in MDA-MB-231 cells. The proliferation ability of breast cancer MDA-MB-231 cells is inhibited after transfection with miRNA-101-mimic.