Abstract: Objective: To observe the influence of ¹³¹I therapy on the thyroid weight and function of patients with Graves’ disease.Methods: The thyroid weight was determined by coloural ultrasound and 60% weight was used as target.The ¹³¹I dosage for each gramme of thyroid tissue was decided accordind to the patients’ age:patients between 17-29 years were administered 2.22-2.96 MBq/g,30-50 years 2.96-3.7 MBq/g and over 50 years 3.7-5.55 MBq/g.Results: The thyroid weight of thirty-six patients decreased from（74.00±37.6）g to（34.34±16.56）g（P<0.01）,and forty-four patients’ TT₃ and TT₄ returned to nomal level after half a year’s treatment.Conclusions: ¹³¹I can reduce the thyroid weight and maintain the thyroid function in patients with Graves’ disease.