Abstract: Objective To study the correlation between gastric bacterial number and pH value and whether hypochlorhydria can cause lower respiratory tract infection. Methods pH value was measured in gastric fluid from 66 patients with chronic gastritis.The number of aerobic and anaerobic bacteria was calculated respectively after gastric tissue was cultured.The patients were asked whether they administered gastric acid inhibiting drugs and had lower respiratory tract infection 6 months before and after gastric tissue culture. Results The number of aerobic（P=0.000）and anaerobic（P=0.001）bacteria was positively correlated with gastric pH value.Lower respiratory tract infection was closely related with hypochlorhydria（P=0.023）. Conclusion The number of gastric bacteria is positively correlated with pH value in human stomach.Lower respiratory tract infection is closely related with hypochlorhydria.