Abstract: Objective: The objective of this study was to identify the impact of oral care practices on oral health status of patients in intensive care unit and the incidence rate of ventilator-associated pneumonia. Method: This clinical trial recruited 100 participants who were randomly assigned to a control group (receiving oral care by nurses) and an intervention group (receiving systematic care by the researcher) during 2015-2016. Beck Oral Assessment Scale was used to determine the required number of times for receiving oral care with regard to patient’s oral health in the intervention group. Each care included adjusting endotracheal tube cuff pressure, brushing with toothpaste, using antiseptics and moistening the lips. The oral cavity was examined using BOAS and Mucosal-Plaque Score, and Clinical Pulmonary Infection Score was used for detecting pneumonia. Results: The BOAS scoring showed significant differences between the two groups from the first to fifth day (P<0.001). The mucosal-plaque index was significantly different between the two groups from the third day to fifth day (P<0.001). The incidence rate of pneumonia on the third and fifth day was 10% (5) and 14% (7) in the control group, and 4% (2) and 10% (5) in the intervention group, respectively. The Fisher test did not show significant difference (P=0.538), however, the incidence rate in the intervention group reduced compared with the control group. Conclusion: Although following a systematic oral care program could not significantly decrease the incidence of ventilator-associated pneumonia in critically ill patients compared to the conventional oral care practices, it significantly improved the oral health and mucosal-plaque index.