Objective : Although hypothyroidism is a common disease in the endocrinology system, it is reported that there are a lot of difficulties in treating it effectively. Aconiti Ra얕 traditionally has been used in treatment of coldness, fatigue, and bradycardia. In this study, we investigated the therapeutic effects of Aconiti Radix on hypothyroidism rat model induced by 6-propyl-2-thiouracil (PTU). Methods : Two-month-old rats were used with administration of PTU which induced hypothyroidism in the rats. After 2 weeks, Aconiti Radix and thyroxine were administered, respectively. The body weights were measured every week. After 4 weeks, the blood samples of all rats were taken from their hearts. They were analyzed biochemically and $T_4$ (thyroid hormone) & TSH (thyroid stimulating hormone) was measured by ELISA kits. Results : In comparison with normals, controls showed hypothyroidism with significantly low $T_4$ and high TSH the statistics. In Aconiti Radix administration groups significantly increased $T_4$ was observed in the statistics and its effects were dose-dependent. There was no difference statistically in TSH of Aconiti Radix treatment groups from controls, nor were statistical differences observed significantly in biochemical labs and weight of each group. Conclusions : These findings suggest that Aconiti Radix protects thyroid cells and makes thyroid cells produce thyroid hormones. It is also very safe in the view of liver, kidney function, and other metabolism. It may be a useful agent for treating hypothyroidism.