Invasion and metastasis are the hallmarks of malignant tumors differing from benign diseases. Most of cancer deaths are mainly due to the development of tumor metastasis rather than primary lesions. Therefore, understanding the molecular mechanisms of invasion and metastasis that take place in malignant cells will provide insight into the development of new therapeutic approaches. However, the complex processes of tumor invasion and metastasis pose a great difficulty in studying their molecular bases. Recent studies have shown that a class of endogenous small nonprotein coding RNAs, termed microRNAs (miRNAs), play an important role in invasion and metastasis of several malignancies, such as breast, liver, prostate and colorectal cancers. In this review, we will summarize the recent studies on the miRNAs in tumor invasion and metastasis, and accentuate the role of miRNAs in elucidating molecular mechanisms of these important processes.