Obejctive: To evaluate clinical characteristic and mortality of acute respiratory failure (ARF) in Korean intensive care units (ICUs). Methods: We used data from the "Validation of simplified acute physiology score 3 in Korean ICUs" (VSKI) cohort study. A prospective multicenter cohort study was performed between July 1st, 2010 and January 31th, 2011. A total 4,074 critically ill patients were enrolled in 22 ICUs. Among them, a total of 741 cases were PaO2/FiO2 less than 300 at admission of intensive care units. Results: Patients were divided acute hypoxemic respiratiory failure (AHRF) and acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Baseline characteristics were not significantly different between two groups except prevalence of infection. The 28-day mortalities were 28.7% for AHRF and 33.3% for ALI/ARDS (P=0.38). The 28-day mortalities were 22.2% for ALI and 35.7% for ARDS (P=0.16). Conclusion: There was no significant difference of mortality rates between ALI/ARDS and AHRF in Korean ICUs.