The aim of the work was to study the superoxide dismutase and catalase activity, tocopherol and retinol content in the tissues of the 8 diving and 6 terrestrial species of mammals. Antioxidant system status was determined in liver, kidneys, heart, lungs, spleen and skeletal muscle. The antioxidant protection of the most diving animals is carried out by high enzymatic activity in the tissues. The total activity of antioxidant system in the tissues of diving animals was higher than in the terrestrial animals. However, the high activity of the antioxidant system typical also for terrestrial animals, leading an active lifestyle all year (sable, marten). At the same time, the enzymes activity in the most tissues otter was considerably lower compared with other species. The highest vitamin A and E content found in the tissues of predators, in the rodents and insectivores it was significantly below. It is shown that in the animals with different systematic conditioning the antioxidant protection could be exercised or through high enzyme activity in tissues, or due to nonenzymatic antioxidants. The enzymes and nonenzymatic antioxidants level in the tissues and organs of the diving and terrestrial mammals, obviously, should take is formed during the evolution of the single complex, which provides the high efficiency of the metabolic systems functioning in the adapting conditions.