Breast cancer is one of the most common malignant tumors among females, and can seriously affect the physical and mental health and even threaten the lives of women. Recently, research has demonstrated that microRNAs (miRNAs), as a new method of regulation, have been shown to have oncogenic and tumor‑suppressive functions in human breast cancer. Detection of their expression may lead to the identification of novel markers for breast cancer. In the present study, we firstly detected miR‑340 expression and found lower expression of miR‑340 in 6 human breast cancer cell lines by using RT‑qPCR. Then by using wound healing assay and Transwell migration and invasion experiments, we focused on the role of miR-340 in the regulation of tumor cell migration and invasion, exploring the relationship between them. The results revealed that induction of miR‑340 expression was able to suppress tumor cell migration and invasion, whereas knockdown of miR‑340 expression promoted breast cancer cell migration and invasion. At the gene level, MYO10 (myosin X), as a direct miR‑340 target gene, mediated the cell migration and invasion. Finally, we verified our research further at the tissue specimen level and in animal experiments. In brief, miR‑340 plays an important role in breast cancer progression. Thus, miR‑340 may be further explored as a novel biomarker for breast cancer metastasis and prognosis, and potentially a therapeutic target.