Small animal patients, similar to human infants, develop hypothermia more rapidly inder anesthesia than asult patients because of their relatively large body surface area in relation to their body weight. Current methods for preventing hypothermia, including infusions of warmed fluids and blood, inspired gases, heating mattresses, skin-surface insulation, etc., are either ineffective or impractical in small sized patients. Our study fuund that four-paw active warming (40℃) could help reduce the degree of hypothermia in rats under general anesthesia and reduce the recovery time from anesthesia.