Abstract: MicroRNAs (miRNAs) are small non-coding RNA molecules with 21 to 24 nucleotides in length, which can regulate post-transcriptional gene expression by interacting with the 3' untranslated regions of the target mRNAs. MiRNAs are widely expressed in eukaryotic cells and involved in a variety of biological processes, such as in the development, differentiation, proliferation, and apoptosis of cells. They also play essential roles in cell cycle regulation, migration, and tumor development. MicroRNA expression varies in different human tumors and is considered a powerful potential biological indicator in the development, diagnosis, treatment, and prognosis of cancers. Breast cancer is one of the most common malignancies, and miRNA expression has been found to be differentially expressed in various types of breast cancer. The expression and function of some miRNAs involved in breast cancer development, metastasis, and treatments are briefly summarized in this review.