To understand the adaptational strategy of Korean chipmunks (Tamias sibiricus) to cold temperature, blood and serum properties, and thyroid gland activity of cold-exposed chipmunks were examined. The number of erythrocytes and hemoglobin concentration increased, but platelets decreased in cold-exposed chipmunks compared with warm chipmunks. Serum total protein levels increased at early phase of cold-exposure, and decreased thereafter. Plasma glucose levels showed a transitory increase in cold temperature. Although there was significant decrease in serum total thyroxine level in cold-exposed chipmunks, serum total triiodothyronine level changed little. Histological analysis of thyroid glands demonstrated decreased thyroid activity, suggesting that differences in the blood and serum properties between the warm and cold-exposed chipmunks may be due to the different metabolic strategy associated with cold temperature.