This report describes the features of the anti-ulcer effect of Oren-gedoku-to (OGT, a traditional Chinese medicine) and its component herb drugs. Coptidis rhizoma and Phellodendri cortex given orally dose-dependently inhibited the appearance of ethanol-induced gastric hemorrhagic lesions in a dose range of 25-100 mg/kg, but the formation of the lesions was not prevented by Scutellariae radix or Gardeniae fructus at the same doses. Coptidis rhizoma, Phellodendri cortex and Gardeniae fructus inhibited the gastric potential difference (PD) reduction induced by ethanol, whereas Scutellariae radix did not prevent the decrease in the PD reduction caused by ethanol. Phellodendri cortex, Scutellariae radix and Gardeniae fructus had no significant influence on the basal PD, while Coptidis rhizoma increased the basal PD. The four herb drugs prevented gastric acid secretion induced by 2-deoxy-D-glucose, but the three drugs except for Phellodendri cortex showed little effect on pentagastrin-stimulation. These results suggest that the gastric mucosal protection by OGT is ascribed to Coptidis rhizoma and Phellodendri cortex, and its antisecretory effect is due to the four drugs.