Epithelial-mesenchymal transitions is a process in which epithelial cells lose polarity, alter cytoskeletal structure and composition and implement a transcriptional program that facilitates the mobile phenotype of mesenchymal cells. It is a foundemental process governing morphogenesis in multicellular. Cytokine transforming growth factor-β (TGF-β), transcription factor snail, metalloproteinases MMPs, viral oncogene can induce epithelial-mesenchymal transition (EMT).EMT of tumor cells further reveals invasion, metastasis and signal transduction mechanism,lays the foundation to find anti-tumor therapeutic target.