Metastasis is the most significant process affecting the clinical management of cancer patients and occurs in multiple sequential steps. However, the molecular pathways underlying each step still remain obscure. Recent research has shown that there is a microRNA (miRNA) network that functions as a regulator of tumor metastasis. In this paper, we review the role of miRNAs in tumor metastasis, including control of epithelial-mesenchymal transition, regulation of metastasis-associated genes and epigenetic alterations. More information on miRNAs will promote a better understanding of the molecular mechanism of metastasis.