Most of the critically ill patients undergoing mechanical ventilation need endotracheal tube to keep their airway open, Existence of endotracheal tube leads to blockage of spontaneous removal of secretions from endotracheal tree, resulted from suppression of cough reflex and an increase in mucus secretions, The aim of this study was to determine the effect of closed versus open suction system on the cardiopulmonary parameters of mechanical ventilated patient. Design: Comparative study research design was utilized in the study. Sample: A purposive of 60 adult patients aged 18 years or more from both gender divided to two groups open & closed suction group who was admitted during the study period on mechanical ventilation and met the inclusion criteria. Setting: Data were collected from Intensive Care Units at General Fayoum Hospital. Tools: Data was collected utilizing two designed tools (1) Interview assessment questionnaire which includes demographic characteristics, Present medical characteristics, Mechanical ventilator assessment questionnaire, Mechanical ventilator parameter assessment questionnaire, suction characteristics assessment questionnaire (2) Physiological outcomes follow up sheet which include Cardiac Parameter and Respiratory Parameter. The results revealed that, closed suctioning system has fewer physiological disturbances on physiological outcomes stability than an open suctioning system for mechanically ventilated patients .Conclusion: the implementation of closed suction system among the study group, according to the results of basic assessment, has been fewer physiological disturbances on physiological outcomes stability than an open suctioning for mechanically ventilated patients. Recommendation: This study should be repeated in a large study sample and different settings to compare the most effective method of suction.