Abstract: Objective: To clarify the relationship between blood group ABO and duodenal ulcer(DU)in patients with H.pylori(Hp)infection.Methods: The blood type of 80 patients with DU and 1 061 healthy controls were determined.The age of disease onset in DU patients with different blood types was compared and the Hp infection rate was determined by rapid urinase test.Results: Fifty six point three percent of the patients in DU group were of blood group O,which was significantly higher than the normal blood group distribution rate(28.7%)in healthy population(P<0.005).However,there was no statistical difference in the average age of disease onset or in the Hp infection rate(P>0.05)among different blood groups.Conclusions: Patients with blood group O doesn’t acquire DU by Hp infection or stronger gastric acid secretion.