The epithelial-mesenchymal transition (EMT) plays physiologic roles in the embryogenesis, wound healing, and tissue regeneration. In terms of pathological direction, it causes organ fibrosis, cancer development, progression, metastasis, and chemoresistance. Recently, the underlying mechanism of EMT and many kinds of EMT regulators have been identified. Pharmaceutical treatment strategies which target EMT pathway could be applied for the prevention of tissue fibrosis and cancer progression. In the field of gastroenterology, profuse evidences have been collected about the critical roles of EMT in cancers of the gastrointestinal tract, liver, and pancreas and hepatic fibrosis. However, EMT varies widely among cancer types, and much remains to be identified about the main regulators of EMT in a specific disease. In this review, we present recent research results regarding the roles of EMT in cancers and organic fibrosis, especially in the area of gastroenterology. (Korean J Gastroenterol 2010;56:69-77)