In this study, we evaluated the gastric protective activities of mokdanpi in vitro . Further, we used experimental ulcer models to identify the active ingredients of mokdanpi. As a preliminary evaluation of mokdanpi ethanolic extract and its ingredients, we assessed its radical scavenging activities. In addition, its antimicrobial activity against Helicobacter pylori ( H. pylori ) was investigated. The antiulcerogenic activity of the active ingredients was evaluated in pylorus-ligated rats, an HCl/ethanol-induced and an absolute ethanol-induced ulcer model. We confirmed the scavenging effect of the ethanolic extract of mokdanpi and its ingredients against 2,2-diphenyl-1-picrylhydrazyl, nitric oxide and superoxide radicals, and we demonstrated that mokdanpi could inhibit the colonization of H. pylori . In an HCl–ethanol-induced ulcer model, gallic acid and catechin (100 mg/kg) inhibited 40.6% and 41.7% of gastric lesions, respectively. Catechin (100 mg/kg) significantly reduced ( p <0.05) the gastric secretion induced by pylorus ligature in rats in comparison to the control group. Gallic acid (100 mg/kg) significantly increased ( p <0.05) the mucus contents in an ethanol-induced ulcer model. The antioxidant ingredients (catechin and gallic acid) present in mokdanpi play a major role in antiulcerogenic activity, and demonstrate novel activity against H. pylori .