Background: Ventilator-associated pneumonia (VAP) is a common nosocomial infection, which results in longer hospitalization, increased treatment costs, and higher mortality rates. One major cause of VAP is colonization and microaspiration of oropharyngeal secretions following the formation of dental plaque, which is due to poor oral hygiene and failure to mechanically remove these microorganisms from the teeth. This study was conducted to determine the effect of brushing teeth with distilled water on the incidence of VAP in patients admitted to intensive care unit (ICU). Materials and Methods: In this randomized clinical trial, 168 intubated patients, who had at least 20 teeth were randomly assigned to two groups. In the experimental group, the patients’ teeth were brushed twice a day with a children’s toothbrush and distilled water in addition to the routine oral care. The clinical pulmonary infection score (CPIS) was used to diagnose VAP. The data were analyzed using SPSS version 16 software. Results: A total of 38.6% of the patients in each group developed VAP. There was a significant difference in incidence of VAP on day five between the two groups (p <0.05). The incidence of VAP had a significant relationship with smoking (p <0.001), underlying diseases (p <0.001), duration of hospitalization (P=0.002), and age (p <0.001). Enterobacter was the most common microorganism identified in both groups. Conclusion: According to our results, tooth brushing twice daily with distilled water reduced the incidence of VAP in patients admitted to the ICU. Therefore, it is recommended that nurses caring for ventilator-dependent patients brush the patients’ teeth with distilled water as a part of their routine oral care.