Objective: This study aimed to explore the regulatory mechanism of miR-139-5p on the biological characteristics of breast cancer cells by targeting Collagen type XI alpha 1 chain (COL11A1).Method:GEO2R was used to identify the differentially expressed genes (DEGs) of breast cancer in GEO database. miRDB, miRanda and Target Scan databases were used to predict the miRNAs that regulate COL11A1. qRT-PCR was used to detect the expressions of COL11A1 and miR-139-5p in breast cancer cells, and western blot was used to detect the protein level of COL11A1. RNA binding protein immunoprecipitation assay was employed to test the targeted relationship between miR-139-5p and COL11A1, which was further verified by dual-luciferase reporter gene assay. CCK-8 assay was performed to detect the cell proliferation, and flow cytometry was carried out to examine the cell apoptosis. Moreover, western blot was used for the detection of caspase-3, Bax and Bcl-2 protein levels. Results: A total of five DEGs were screened from the GEO database, of which COL11A1 was the only highly expressed in breast cancer. According to the database analysis, we predicted that miR-139-5p was muchlikely to target the expression of COL11A1. MiR-139-5p was poorly expressed in breast cancer cells and targeted inhibited COL11A1. Silencing COL11A1 or overexpressing miR-139-5p both could inhibit the proliferation and promote the apoptosis, while overexpressing thetwo factors simultaneously could reverse such effect. Conclusion: Overexpression of miR-139-5p inhibits the proliferation and promotes the apoptosis of breast cancer cells by inhibiting the expression of COL11A1. ©2020 the Author(s).