Free radical homeostasis parameters of rat’s brain mitochon- dria under conditions of sodium nitrite administration at the peak of hypoxia had been studied. Prior to study experimental animals have been divided into two groups depending on resistance to hypobaric hypoxia. In brain mitochondria of high-resistant to hypoxia rats increase of the nitrites-ions contents and also in- tensification of pro- and antioxidative processes were registered in comparison with the control group. Decrease of all investgated free radical homeostasis parameters in brain mitochondria of low-resistant to hypoxia animals in comparison with the control group was determined. Administration of pro-hypoxic factor in toxic dose allowed us to reveal specific peculiarities of redox processes development in the brain mitochondria of experimen- tal animals with different resistance to hypoxia.