MicroRNAs (miRNAs) are small noncoding RNA molecules present in all cell types, with sizes that vary from 18 to 28 nucleotides. miRNAs play significant roles in several biological processes, including development, differentiation, metabolism, initiation, and progression of cancer. In recent years, considerable research has been directed towards identifying miRNAs in peripheral blood from circulating tumor cells and disseminating tumor cells. Because these circulatory miRNAs are very stable and reproducible, their identification could be useful as prognostic markers as well as therapeutic agents for many cancers such as breast cancer. In this article, we review the role of specific circulatory miRNAs in breast cancer, with particular emphasis on their clinical importance.