Abstract: Objective To explore the function variation of mitochondria in the rat brain injured by acute hypobaric hypoxia and/or NaCN intoxication.Methods A dult SD rats(male)were divided randomly into normoxic group,acute hypoxia group and prestep adaptation group.The acute hypoxic exposure model was established by exposing the rats to a hypobaric chamber smiulating 4 000 mabove sea level for 3 days.The rats in the prestep adaptation group were continuo usly exposed to hypobaric chamber stmiulating 1 500,2 500,3 000,3 500 and 4 000m,respectively for one day.The rats were in jected with 3.6m g/kg NaCN intra peritoneally.The rats were sacrificed and the brains were isolated at the time of 0.5 and 2h of intoxication.Brain mito chondria were isolated by centrifugation program.HPLC was employed to determine the contents of ATP,ADP and AMP in the mitochondria of the rat brain.Results In normoxic group,acute hypoxia group and prestep adaptation group,ATP content was decreased and ADP and AMP contents were inereased(P<0.05 or P<0.01).The activities of mitochondrial complex Ⅰ and Ⅳ were also decreased.ATP of the acute hypoxia group decreased.ADP and AMP contents were increased compared to these of the normoxic group(P<0.05).Conclusion NaCN intoxication may influence the energy store reduction and the activity of complex Ⅰ and Ⅳ of the brain mito chondria in rats exposed to acute hypoxia.