PURPOSE: Nitric oxide (NO) is a vasodilator and inhaled NO (iNO) is used in acute respiratory distress syndrome (ARDS) to improve alveolocapillary gas exchange. The mechanism to improve oxygenation is likely to redistribute blood flow from unventilated areas to ventilated areas. Though improvement of oxygenation, iNO therapy has not been shown to improve mortality and considered as only rescue therapy in severe hypoxemia. We conducted the study to investigate an efficacy of iNO in trauma patients with severe hypoxemia. METHODS: We reviewed the trauma patients who underwent iNO therapy retrospectively from 2010 to 2014. Degree of hypoxemia was represented as PaO2/FiO2 ratio (PFR) and the severity of patient was represented with sequential organ failure assessment (SOFA) score. Patients were divided into the survivor group and non-survivor group according to the 28-day mortality. RESULTS: A total of 20 patients were enrolled. The mortality of 28-day was 40%. There were no significant differences between survivor and non-survivor group in age, sex, severity of injury, PFR and SOFA score. There was significant difference in initiation time of iNO after injury (p=0.047). Maximum combinations of sensitivity and specificity for timing of iNO therapy were observed using cut-off of 3-day after injury with a sensitivity of 88% and specificity of 75%. CONCLUSION: Though iNO therapy does not influence the mortality, iNO therapy may decrease the mortality caused by respiratory failure in the early phase of trauma.