The experimental study carried out with white rats Wistar trend, which were introduced of sodium nitrate at a rate of 9.6 g/kg of their mass. It follows to the development of considerable activation of lipid peroxidation and depression of antioxidant system in liver. The obtained results permit supposing the significant role of nitric oxide (NO) in liver as a factor resulting in accumulation of peroxidation products. The research has stated that the use hyperbaric oxygenation (HBO) prevents considerable activation of lipid peroxidation and the decrease of antioxidant enzyme (catalase and superoxide dismutase) activity. The results permit supposing that the effect HBO is connected with the decrease of the rate of reduction of nitrate-ions to NO.