Background:In various studies, Cydonia oblonga Miller (quince) has been reported to have many properties such as antioxidant and anti-ulcerative effects. This study has aimed to investigate the protective effects of quince aqueous extract (QAE) and quince hydroalcoholic extract (QHE) on gastric ulcer caused by indomethacin and the relevant macroscopic, histopathology, and biochemical factors in rats.Methods:Ten groups of male Wistar rats, six in each, were used in this study. These groups included: normal (distilled water), control (distilled water + indomethacin), reference (ranitidine or sucralfate + indomethacin), and test groups (QAE or QHE + indomethacin) treated with three increasing doses (200, 500, and 800 mg/kg). Extracts and drugs were given orally to rats 1 h before injecting the indomethacin (25 mg/kg, intraperitoneally). Six hours later, the abdomen of rats was exposed, its pylorus was legated, gastric acid content was extracted, and its pH and the amount of pepsin secreted were measured by Anson method. Then, histopathology indices, ulcer area, ulcer index, and myeloperoxidase (MPO) activity were measured in gastric mucus.Results:Both extracts of quince were effective to reduce the acidity of stomach and pepsin activity. Compared to control group, the average of enzyme activity of MPO was significantly declined in all treated groups. Control group had the highest level of gastric ulcer indices including severity, area, and index while the evaluated parameters had decreased in all extract treated groups although it seems that QAE was somewhat more effective.Conclusions:Protective effect of QAE and QHE on gastric ulcer was done by undermining offensive factors including decreasing the secretion of gastric acid and pepsin activity and by strengthening the protective factors of gastric mucus including antioxidant capacity.