On experimental gastric ulcer models induced by 0.6mol/L HCl, ethyl alcohol or ligation of the pylorus, the preventive effects of unprepared oyster shell, calcined oyster shell 1(900 degrees C, 1h), calcined oyster shell 2(350 degrees C, 8h) were compared in Wistar rats. Results showed that antagonistic effects of calcined oyster shell 1 to the drug pathogenesis of peptic ulcer and the incidence of peptic ulcer after ligation of the pylorus were markedly greater.