Therapeutic mechanisms of hyperbaric oxygen therapy (HBOT) are based on elevation of both the partial pressure of oxygen and hydrostatic pressure. It has been reported that HBOT supply much amount of oxygen and might prevent from brain tissue after global ischemia in patients with post-cardiac arrest syndrome(PCAS). On the other hand, high levels of oxygen produce reactive oxygen species(ROS). ROS occurs secondary brain damage after ischemia. The clinical evidence of HBOT has not been established. In this paper, we review some reports about the advantages and disadvantages of HBOT after global ischemia with PCAS.