Introduction: The problem in patients who are intubated with endotracheal tube is the occurrence of accumulation of secretions. One of the actions to reduce the secretion is closed suction. This research monitors the patient's oxygensaturation and also reveals the effect of closed suction on oxygen and AaDO2 saturation (alveolar-arterial oxygen difference) in patients who were mechanically ventilated in the Intensive Care Unit (ICU) of Dr. Kariadi Hospital. The design of this study uses pre experiment. Methods: The research process has been carried out on April 2, 2019 until May 26, 2019 in the Intensive Care Unit with a total sampling technique, on 15 respondents. Result: The results of the study showed that there was effect of closed suction technique on the value of oxygen saturation in patients with mechanical ventilation (p-value = 0.010). Conclusion: Closed suction can lead to decrease of air volume in the lungs up to 1200 ml. So hyperoxygenation must be done before closed suction as it can reduces the incidence of hypoxemia by 49%. Before closing the suction, it is recommended to do hyperoxygenation.