Mammalian hibernation is a state of seasonal heterothermy and survival strategy. The hibernation consists of long periods of deep torpor interspersed by brief interbout arousal periods. During torpor, metabolic rate is profoundly depressed and core body temperature decreases to near ambient temperature. However, these functions are promptly restored to the basic level upon arousal, and a quick restoration of blood flow accompanied by an increased mitochondrial respiration and oxygen usage results in elevated generation of reactive oxygen species (ROS) in mammals. However, no oxidative damage is found in the tissues of hibernators during a prolonged period of hibernation. Small mammalian hibernators have, therefore, been considered to be the best model of the anti-oxidative damage. In this paper, the adaptation mechanisms of oxidative stress to hibernating mammals are reviewed with respect to the generation of oxidative stress, the source of ROS and antioxidant defense.