ABSTRACT Objective: To investigate the expression and mechanism of microRNA (miRNA)-613 in breast cancer. Methods: A total of 91 specimens of breast cancer tissue were collected from Nanchong Central Hospital between May 2017 and May 2018. Quantitative real-time PCR (qRT-PCR) was used to estimate miRNA-613 expression levels in breast cancer and adjacent tissues and breast cancer ( cells MDA-MB-231, MDA-MB-468, and MCF-7) and normal breast epithelial (HBL-100) cell lines. Based on these data, the relationship between miRNA-613 expression and clinicopathological characteristics and prognosis in breast cancer patients were analyzed using the cancer genome atlas (TCGA) database. A dual-luciferase reporter assay was used to detect the binding of miRNA-613 to the 3'UTR of SOX9. Effects on cell proliferation and cell invasion and migration upon transfection of MDA-MB-231 cells with miRNA-613 mimics were detected by the CCK-8 assay and Transwell invasion and migration assays, respectively. In addition, Western blot was used to estimate the expression levels of SOX9, β-catenin, E-cadherin, and Vimentin in the transfected cells. Results: The expression of miRNA-613 in breast cancer tissues was significantly lower than that in adjacent tissues (P<0.05) and was found to be closely related to TNM stage and lymph node metastasis (P<0.05). TCGA survival data showed that miRNA-613 expression was not related to the overall survival rate of breast cancer patients (P>0.05 ). The expression of miRNA-613 in breast cancer cell lines was significantly lower than that in the normal breast epithelial cell line (P<0.05). Similarly, the expression of miRNA-613 in highly invasive metastatic breast cancer cell lines (MDA-MB-231 and MDA-MB-468) was significantly lower than that in the metastatic breast cancer cell line MCF-7 with lower invasion ability (P<0.05). The dual-luciferase reporter assay showed that miRNA-613 could specifically bind to the 3'UTR of SOX9. Upregulation of miRNA-613 expression could inhibit the proliferation, invasion, and migration of MDA-MB-231 cells (P<0.05). This was associated with the downregulated expression of SOX9, β-catenin, and Vimentin (P<0.05) and upregulation of E-Cadherin expression (P<0.05). Conclusions: The expression of miRNA-613 was decreased in breast cancer tissues and cell lines. MiRNA-613 may inhibit the proliferation, invasion, and metastasis of breast cancer cells and epithelial-mesenchymal transition by regulating the SOX9 and Wnt/β-catenin signaling pathways.