This retrospective study was designed to analyze the early therapeutic outcome of radioiodine therapy in patients with Graves'disease. According to the follow up result after one year treatment, patients were divided into two groups on the basis of whether there was signs of hypothyroidism. 46 patients with hypothyroidism, 60 patients without hypothyroidism were selected randomly. The SAS software was used to assess the outcome of early hypothyroidism and the thyroid weight, the peak of 131 I uptake, absorption value by per gram of thyroid tissue, thyroglobulin autoantibody (TGA), and thyroid microsome autoantibody (TMA) levels. Rank sum test, t test and ? 2 test were used to compare the variable parameters between the two groups. Thyroid weight ( P =0 0106) and the peak of 131 I uptake ( t =2 1725, P =0 0321) between two groups had significant difference. The absorption value of the thyroid tissue ( P =0 4420), thyroid autoantibody (? 2 =1 156, P =0 282) had no significant difference between two groups. Patients with smaller gland weight and lower 131 I uptake had an inclination to have early hypothyroidism. Absorption value by per gram of thyroid, TGA and TMA levels had no influence on the outcome of 131 I treatment