Background: The prevention of ventilator-associated pneumonia (VAP) can decrease the duration of mechanical ventilation, length of hospital stay, mortality, and healthcare costs. Objectives: The aim of this study was to compare the effect of the elevation of head of bed (HOB) to 30 and 45 degreess on the incidence of VAP. Methods: This study was a 3 group controlled randomized clinical trial. It consisted of 120 patients who were under mechanical ventilation and hospitalized in the intensive care unit (ICU) from February to July 2016 in the selected governmental hospitals of Iran University of Medical Sciences. The patients were allocated into 3 groups. The patients of intervention groups received interventions consisting of HOB elevation to 30 and 45 degreess for 3 consecutive days. The patients in the control group were in the routine position in the bed for 3 consecutive days. The HOB elevation was measured using the goniometer and recorded by nurses in perticular forms. At the end of the third day, VAP and pressure ulcers were evaluated using the clinical pulmonary infection score (CPIS) as well as Braden scales. The data were analyzed using descriptive and inferential statistics. Results: Statistically significant differences were reported in terms of VAP between the groups of the HOB evelation to 30 degrees (32.50%) and 45 degrees (20.00%) and control groups (52.50%) (P = 0.01). However, the mean scores of pressure ulcer showed no statistically significant differences between the groups (P = 0.625). The greatest change in position was performed by the staff nurses