Objective To study new preoperative preparation for primary hyperthyroidism. Methods Before operation, Lugol solution was used(5～10 getts/time, 3 times/d) for 10 days. On the 7th day, dexamethasone 20?mg was added to 5%～10% glucose solution 500?ml was consecutively used for 3 days before the operation. Results FT 3 fell to normal value after dexamethasone 20?mg was used once, and FT 4 fell to normalvalue after dexamethasone used 3 days. There was no any complication, such as thyroid crisis occurring in this series. Conclusions Dexamelhasone applied before operation as the preoperative preoparation for primary hyperthyroidism is testified a safe and effective method.