Peptic ulcer and gastroesophageal reflux are common acid-peptic related diseases. The pathophysiology of peptic ulcer disease has been centered on an imbalance between aggressive and defensive factors. This study was conducted to examine whether the combined use of omeprazole (CAS 73590-58-6), a proton pump inhibitor, and DA-9601, a novel anti-ulcer formulation of the extract of Artemisia asiatica Nakai, has synergistic effects on various peptic ulcers and gastroesophageal reflux diseases in animal models. An optimal combination ratio of omeprazole and DA-9601 was investigated in an acetic acid-induced ulcer model. In the results, oral pretreatment with omeprazole and DA-9601 (combination ratio, 1:3) significantly reduced alcohol-, indometacin-, acetic acid-, and cysteamine-induced gastrointestinal lesions in a synergistical manner in rats. The combination treatment also significantly attenuated the gross and histopathological lesions in an experimental reflux esophagitis model as compared to the single treatment of omeprazole or DA-9601. In an alcohol-induced gastritis model, the combined treatment resulted in a significant decrease in lipid peroxidation with concomitant increases in glutathione content and prostaglandin E2 level, which was proportional to the inhibitory effect of the combination therapy. These results suggest that the combined therapy with omeprazole and DA-9601, a cytoprotectant, can be beneficial for the treatment of peptic ulcer and reflux esophagitis.