A preoxygenation plays an important role to maintain enough oxygen saturation during rapid sequence intubation. However it is not easy procedure to perform positive pressure ventilation with bag valve mask (BVM) and fitting a mask on patient`s face simultaneously in patients with decreased mentality or respiratory failure. Non-invasive nasal positive pressure ventilator (OptiflowTM) can support oxygenation without intervention via orotracheal route. We conducted an observational cohort study for evaluating a usefulness of non-invasive nasal positive pressure ventilator in rapid sequence intubation. Patients over 18 years old who need for rapid sequence intubation in emergency department were enrolled from April, 2014 to July, 2014. Patients with basal skull fracture or nasopharyngeal obstruction due to trauma were excluded. A non-invasive positive pressure ventilator (OptiflowTM) was used for preoxygenation for 3 minutes with setting of FiO2 1.0 and 50L/min flow rate and this setting was maintained until intubation was done. The maximum SaO2, the elapsed time to reach 100% SaO2 during the preoxygenation, the lowest SaO2, any event declining SaO2 under 80%, and the elapsed time to intubation after preoxygenation. A questionnaire was used for evaluating degree of interfering of non-invasive positive pressure ventilator during intubation. Thirty patients were enrolled and fourteen (46.6%) were male. The oxygen saturation was maintained more than 95% in 28 cases (93.3%). The lowest saturation was 97 (92.5-99)%, the time to reach 100% oxygen saturation was 90 (50-125)seconds. However, there was no case of which oxygen saturation was decreased below initial saturation during intubation. The elapsed time for intubation was 13 (10-15) seconds and degree of interfering intubation was 1 (0-1) in 10-point Likard scale in the questionnaire survey for physician. Applying a non-invasive nasal positive pressure ventilator can reduce risk of desaturation in rapid sequence intubation.