Background: If not done properly, suction causes complications such as hypoxia, cardiac arrhythmias or even death. Suction is being used in most hospital wards. Closed Suction appears to have fewer side effects, although studies have reported dissimilar results.Aim: The aim of this study was to compare the effect of open (control) with closed (test) endotracheal suctioning on patients’ Hemodynamic state.Methods: This study was a randomized clinical trial in 86 patients admitted in the ICU of Besat hospital of hamedan in 2013, being divided into two groups: open (control) and closed (test) endotracheal suctioning.Systolic and diastolic blood pressure, mean arterial pressure (MAP), heart rate, arterial O2 saturation (SPO2), respiratory rate and the incidence of disrrythmia were recorded in patients' questionnaires immediately, and afterwards 2 and 5 minutes after endotracheal suctioning by open and closed methods. Data analysis was performed by Repeated Measure ANOVA, t test, chi-square and Fisher's exact test.Results: A total of 102 patients were included in the study. Sixteen patients were excluded from the study and data from 86 patients were analyzed. No statistically significant differences in age (15/0P=) and sex (33/0P=) were found between the two groups.Hemodynamics index in two groups was similar before the suctioning (P>0.05). In the open group, there was an increase in diastolic blood pressure (P=0.017), mean arterial pressure (P=0.019), heart rate (P=0.003) and respiratory rate (P<0.0001) immediately, 2 and 5 minutes after suctioning in comparison to the closed group (P>0.05). Systolic blood pressure, SPO2 and incidence of disrrythmia were similar in the two groups.Conclusion: Endotracheal suctioning by closed method had lower effects on patients' Hemodynamic status rather than the open system. Hence, closed endotracheal suctioning is recommended in the ICU.