Quercetin and its sugar conjugates are the most abundantly distributed bioflavonoids and represent the largest proportion of flavonols in the plant kingdom. The present study was undertaken to demonstrate the effect of quercetin on the role of reactive oxygen species (ROS) in the development of gastric ulcers in rats. Administration of quercetin in doses of 50, 100 and $200;mg;kg^{-1}$ twice daily for 5 days, showed dose dependent significant protection against ethanol (EtOH), aspirin (ASP), cold-restraint stress (CRS) and pylorus ligation (PL) -induced gastric ulcer models and the results were comparable with those elicited by sucralfate. The thiobarbituric acid reactive substances in the stomach mucosa, an index of lipid peroxidation and regulation of plasma corticosterone were significantly increased in CRS-induced gastric ulceration. The queroetin $(100;mg;kg^{-1})$ and reduced glutathione effectively inhibited gastric lesions induced by CRS with a significant decrease in the lipid peroxidation and plasma corticosterone. These results indicate that quercetin a bioflavonoid exerts its antiulcer effect in light of free radical scavenging and plasma corticosterone in cold restraint stress ulcers.