Objective:　To study the changes of partial pressure of oxygen in brain tissue (PbtO2) and brain temperature (BT) in patients in acute phase of severe head injury, and to study the effect of mild hypothermia on PbtO2 and BT. 　　Methods:　The PbtO2 and the BT of 18 patients with severe head injury were monitored, and the patients were treated with mild hypothermia within 20 hours after injury. The rectal temperature (RT) of the patients was kept on 31.5-34.9℃ for 1-7 days (57.7 hours±28.4 hours averagely), simultaneously, the indexes of PbtO2 and BT were monitored for 1-5 days (with an average of 54.8 hours±27.0 hours). According to Glasgow Outcome Scale (GOS), the prognosis of the patients was evaluated at 6 months after injury. 　　Results:　Within 24 hours after severe head injury, the PbtO2 was significantly lower (9.6 mm Hg±6.8 mm Hg, 1 mm Hg=0.133 kPa) than the normal value (16-40 mm Hg). After treatment of mild hypothermia, the mean PbtO2 increased to 28.7 mm Hg±8.8 mm Hg during the first 24 hours, and the PbtO2 was still maintained within the range of normal value at 3 days after injury. The BT was higher than the RT in the patients in acute phase of severe head injury, and the difference between the BT and the RT significantly increased after treatment of mild hypothermia. Hyperventilation (the partial pressure of carbon dioxide in artery (PaCO2)≈25 mm Hg) decreased the high intracranial pressure (ICP) and significantly decreased the PbtO2. 　　Conclusions:　This study demonstrates that PptO2 and BT monitoring is a safe, reliable and sensitive diagnostic method to follow cerebral oxygenation. It might become an important tool in our treatment regime for patients in the acute phase of severe head injury requiring hypothermia and hyperventilation.