Objective The effect of acidity and severity of gastric atrophy on Helicobactor pylori (H.pylori) colonization was studied. Methods 95 patients with chronic atrophic gastritis (CAG) and positive H.pylori test were categorized into groups.Group 1,48 cases having moderate atrophic antritis with various degrees of fundic atrophy.Group 2,47 cases having mild fundic atrophy with various degrees of antritis. Assessment was made of basic and maximum acid output (BAO, MAO ) as well as of gastrin. H.pylori was tested with Warthin-Starry staining. Results In group 1, H.pylori colonization reduced significantly (P0.05) was found between patients with severe and moderate atrophy in fundus, while H.pylori colonization declined more markedly (P0.05) between cases with moderate and severe antritis,whereas H.pylori colonization reduced more significantly in the latter than the former (P