Background: The prevalence of intra-abdominal hypertension in ICU patients is about 50% and can be affected by changing the position of the patients. This study aimed to investigate the relationship between changing patient positions in bed with intra-abdominal pressure and mean arterial pressure among mechanically ventilated patients in ICU. Methods: This study was a clinical trial conducted on 68 patients admitted in intensive care units of Imam Khomeini hospital of Urmia city, Iran. The patients were selected through convenience sampling based on the inclusion criteria. In this study, the effects of changes in five positions (0, 15, 30, 45, left and right lateral position with 30 degrees) on the mean arterial pressure was evaluated. Statistical tests such as chi square and repeated measures ANOVA were used as well. All analyzes were performed using SPSS 21. Results: In this study, there were 24 men (35.3%) and 44 women (64.7%). The mean age, weight and height of patients were 70.35±16.98 years, 75.76±9.77 kg and 168.82±8.14 cm, respectively. There was no significant difference regarding intra-abdominal pressure by gender (p<0.05). There was a significant difference regarding intra-abdominal pressure between first, second, fourth and fifth measurements (p<0.001). There was a significant difference regarding mean arterial pressure between first, second, third, fourth and fifth measurements (p<0.001). Significant differences were observed between the fifth and fourth mean arterial pressure measurements as well (p<0.001). Conclusion: According to the results of this study, the changing of patient's body position from supine to higher positions lead to the increase of intra-abdominal pressure.