Reactive oxygen species (ROS) are produced as by-products of the normal metabolism of the cell. ROS are generated in response to ultraviolet radiation, smoking, alcohol, nonsteroidal anti-inflammatories, ischemia-reperfusion, chronic infections and chronic inflammatory disorders. Disruption of the normal homeostasis of the cell, due to changes in redox homeostasis can lead to the development of cardiovascular diseases, neurodegenerative diseases and cancer. The production of ROS in the gastrointestinal tract (GI) and their role in the pathophysiology and pathogenesis of gastrointestinal diseases have not been studied sufficiently. Despite the protective barrier provided by the digestive mucosa, different molecules which may be present in the content of GI,as well as various pathogens can cause oxidative damage and inflammatory response in the intestinal mucosa and the immune cells. Pathogenesis of various GI diseases, including ulcerative lesions, cancer, and inflammatory bowel diseases are attributable in part to oxidative stress. In the plasma of patients, in the context of the sequence gastro oesophageal reflux-oesophagitis-metaplasia-dysplasia-adenocarcinoma, have been found simultaneous formation of DNA adducts and increased myeloperoxidase concentration, which are associated with oxidative stress, decreased antioxidant capacity (decreased glutathione concentration).These findings support the role of oxidative stress in the pathogenesis and malignant transformation.