Hypothermic conditions of homoisothermic organisms are characterized by the activation of free-radical processes in tissues. The intensity of these processes occurring at hypothermia is less well understood. The essential increase in heart rate, breathing, blood flow velocity, and metabolic processes during warming must stimulate the generation of reactive oxygen species and oxidative modification of biomolecules. We study the levels of peroxidation markers of lipids (by malondialdehyde) and proteins (by carbonyl groups) in blood plasma and erythrocytes as well as the activity of erythrocyte antioxidant enzymes of rats after deep hypothermia (the temperature in the rectum was 20°C) and self-warming dynamics. A maximum warming rate (0.016°С/min) was revealed over the body temperature range of 22–33°С, below and above these temperatures a warming rate was essentially lower. The warming of rats resulted in a total protein content reduction which negatively correlates (r = –0.967; р<0.05) with a middle molecular peptide level. The deep hypothermia decreased the intensity of oxidative modification of lipid and proteins in blood plasma and red blood cell membranes, and the activity of red blood cell superoxide dismutase (SOD). Maximum amount of products of oxidative modification of lipids and proteins in plasma and erythrocytes membranes caused by rats’ self-warming was observed at body temperature of 30–35°С. After a complete rats’ warming the intensity of oxidative modification of lipids and proteins in plasma and erythrocyte membranes decreased. The activity of SOD and catalase of erythrocyte substantially increased when body temperature reached 35°С. The obtained data indicate that during self-warming at the body temperature of 30–35°С the oxidative stress appears in blood which requires the use of antioxidant defense.