Background: H pylori is a human gastric pathogen. Chemotaxis is an essential factor in colonization of H pylori, but very little is known about its chemotactic responses at different pH conditions, especially in acidic environment of stomach as its natural habitant. Methods: We first determined survival of H pylori under various pH conditions in the presence and absence of urea. Chemotaxis was then assayed in three strains of H pylori by modified Adler’s procedure, in which potassium bicarbonate was used as an attractant for estimating the chemotactic activity which was compared with phosphate buffer as an inert reagent. Results: H pylori cannot withstand pH 1, but in the presence of urea, it survives in solutions with pH values of2 to 9and remains viable at pH of 3 to 9, irrespective of presence of urea. Maximum chemotactic activity occurred at pH values of 5.5 to 6.5, whereas no chemotaxis was found in solutions with pH 3. Chemotactic activities are increased at pH 3 to 5.5 and reduced at pH 6 to 9, beyond which no chemotaxis was observed. Conclusion: In view of the fact that chemotaxis is severely affected by media pH, it is concluded that the antrum of the stomach is most suitable for colonization of H pylori for which maximum colonization occurs at neutral pH.