Objective To investigate the pathogen and incidence of ventilator-associated pneumonia (VAP) under different pH value of gastric juice,and to explore the endogenous pathogenesis of VAP.Methods Ninety-eight cases were admitted in our neonatal intensive care unit from Dec 2008 to Dec 2010.According to whether VAP happened,they were divided into VAP group (52 cases) and non-VAP group (46 cases).The relation between pH value of gastric juice and the species of pathogenic bacteria in stomach was analyzed.Results The incidence of VAP was 53.1％ (52/98).The pH value of gastric juice affected the species of pathogenic bacteria in stomach.When pH ≤ 4,the major species of pathogenic bacteria were Candida and Gram-positive bacillus; and pH ＞ 4,the major species were Gram-negative bacillus.The incidence of VAP was 34.5％ (10/29) when pH≤4;on the contrary,the incidence was 60.9％ (42/69) when pH ＞ 4.The incidence of VAP at the time of pH ＞ 4 was significantly higher than that of pH ≤4 ( x2 =5.71,P =0.017).Conclusion The pH value of gastric juice is an important factor of the species of pathogenic bacteria in stomach,especially for Gram-negative bacillus,including multi-drug resistant extended-spectrum β-lactamase-producing bacteria.The higher of pH value,the incidence of VAP is higher.