Objectives : The object of this study was to evaluate the effect of Insamyangyoung-tang aqueous extracts (ISYYT) on the propylthiouracil (PTU) induced rat hypothyroidism. Methods : The rats were divided into 6 groups : intact control, PTU control, Levothyroxine (LT 4 ), 500, 250 and 125 mg/kg ISYYT treated groups. In ISYYT treated groups, PTU and ISYYT were administered for 4 weeks after 500, 250 and 125 mg/kg ISYYT were administered for 2 weeks. In LT 4 group, PTU and LT 4 were administered for 4 weeks. The changes were observed : the weigh, serum thyroid hormone levels, serum sex hormone levels, serum lipid profiles, serum liver enzyme levels, liver and testis antioxidant defense system, histopathology of thyroid gland, liver, epididymis, prostate and testis. Results were compared with PTU control group in this experiment. Results : In comparison with PTU control group, 500 and 250 mg/kg ISYYT treated groups showed significant increase of body, thyroid, liver, testis, epididymis and prostate weights, decrease of serum TSH levels with increase of serum T3 and T4 level, increase of serum testosterone and DHT levels with decrease of serum FSH levels, decrease of serum HDL with increase of TG and increase of serum AST levels. Histopathological inspections of hepatic and male reproductive organ damage induced by PTU were improved. And the changes of antioxidant defense system of Liver and testis induced by PTU were improve. There was no significant difference between 125 mg/kg ISYYT treated group and PTU control group in this experiment. Conclusions : The results obtained in this study considered that Insamyangyoung-tang may be effective in hypothyroidism and related organ damages.