The injurious effects of reactive oxygen species on venous tissues and the potential protective role played by green tea polyphenol (GTPP) on human saphenous veins were investigated. Oxidative stress was induced exogenously in the vein segments, either by adding 0.8 or 1.6 M of H2O2, or by using 80 or 160 U/L of xanthine oxidase in the presence of xanthine (0.5 mM). After incubation, the viability of the endothelial cells dissociated from veins and the histology of the veins were evaluated. Due to both types of treatment, a significant decrease in cellular viability, severe morphological changes in the veins, and extracellular structural damage were induced. The H2O2-induced alterations were prevented by preincubating the veins with either 0.5 or 1.0 mg/ml of GTPP for 1 h. When the oxidative stress was induced by xanthine oxidase, cellular viability and venous structure were preserved at the same polyphenol concentrations. These results demonstrate that GTPP can act as a biological antioxidant and protect veins from oxidative stress-induced toxicity.