Background: The pathogenesis of ventilator-associated pneumonia (VAP) is not clearly known. Recently, the role of gastric bacterial colonization has been proposed. The role of gastric colonization with Helicobacter pylori in pathogenesis of VAP was determined by comparing the prevalence of H. pylori in patients with VAP and control participants. Materials and Methods: One hundred and eighteen mechanically ventilated patients were divided into two groups; 59 participants with VAP and 59 without VAP. Serologic tests for H. pylori were registered. Results: Mean age in seropositive patients was significantly higher. About 71.2% in VAP group and 61.01% in controls were IgG seropositive (P = 0.24). IgM seropositivity was 23.73% versus 8.47% in VAPs and controls, respectively (P = 0.024). By increasing the time of intubation, more patients became seropositive for IgM (Pearson's correlation coefficient = 0.4, P = 0.002). Conclusion: IgM seropositivity and serum levels were significantly higher in VAP patients. Furthermore, by increasing the duration of intubation, serum levels for IgM increased significantly.