Gastric mucosal cell proliferation is blamed to be a mechanism in the gastric carcinogenesis. Helicobacter pylori is found to be associated with gastric carcinoma and thought to be a factor in the pathogenesis. Aim of this study was to search the effect of Helicobacter pylori on the gastric bucosal cell proliferation. Forty-six Helicobacter pylori positive gastritis, 33 Helicobacter pylori negative gastritis and 8 normal gastric mucosal endoscopic biopsy material were included in this study. To determine the proliferative activity, Ki-67 (MIB1) immunohistochemical staining was performed. Proliferative activity in Helicobacter pylori positive group was found to be higher than Helicobacter pylori negative and control groups, and the increased proliferative activity was seemed to be associated with both the presence of Helicobacter pylori and the induced activation. In conclusion, Helicobacter pylori induced increase in proliferative activity may be a major factor in gastric carcinogenesis.