Propolis, a natural resinous compound collected from honey bees, contains many biochemical constituents(wax, flavonoids, phenolic compounds, etc.) and has been used in traditional medicines as early as 300 B.C. It was been demonstrated that ethanol, acetylsalicylic acid, ischemia reperfusion, non-steroidal antiin-flammatory drugs and stress induce gastric lesions by promoting the generation of reactive oxygen metabolites. Therefore, some drugs that are capable of scavenging or inhibiting the generation of reactive oxygen radicals might be expected to prevent the gastric mucosal injury. The aim of this study was 1) to examine the antiulcer effect of propolis, 2) to investigate the mechanism of action by determining gastric acid secretion, lipid per-oxidation, mucus content and proton pump ($H^+$/$K^+$-ATPase) activity on gastric mucus in varios experimental models, and finally, 3) to isolate and identify the pure compounds that exert antiulcer activity. Step 2-1 and 2-3 sub-sub fraction shoed a significant reduction of severity of gastirc damage at the dose of 25 mg/kg in various experimental models. We isolated 4 sub-sub-sub fractions by flash column chromatography of Step 2-1 sub-sub fraction and one sub-sub-sub fraction by recrystalization of Step 2-3 sub-sub fraction. The protective effects of propolis sub-sub-sub fraction manifested sifnificant effects in HCl-ethanol induced gastric erosion model and aspirin induced gastric ulcer model. These results showed that the gastric mucosal protective effect of propolis might result from the increase of mucus secretion, free radical scavenging effect as well as the reduction of acid secretion in accordance with the reduction of $H^+$/$K^+$-ATPase activitv. Three compounds were isolated and identified from sub-sub fraction of propolis which showed antiulcer effects. Subsequently, these compounds were identified as a flavonoid, namely, 2-acetoxy-5,7,-dihydroxy-flavanone, galangin and chrysin.