The present invention relates to a Momordicae semen extract effective in the prevention and treatment of gastritis or gastric ulcer and momordica saponin I isolated therefrom. The Momordicae semen extract and the momordica saponin I isolated therefrom is effective in the prevention and treatment of gastritis or gastric ulcer since they prevent the damage of the gastric mucosa caused by alcohols and inhibit the secretion of gastric acid.