Objective To analyze the effects of empirically calculated dose of radioiodine (¹³¹I) therapy on hyperthyroidism of Graves disease. Methods A total of 299 patients with Graves disease underwent the ¹³¹I therapy. The dose of ¹³¹I therapy was determined based on the empirically calculated dose. The therapeutic effect was

evaluated by the thyroid function test after 3 and 6 months of the treatment. Stepwise multiple regression analysis was performed to identify factors that influenced the effect of the ¹³¹I therapy. Results Among 299 cases of Graves disease, the ¹³¹I therapy was effective for 187 (62.5%) cases after being treated for 3 months and the incidence of hypothyroidism caused by the treatment was 84 (28.1%) cases. The ¹³¹I therapy was effective for 248 (83.0%) cases after being treated for 6 months and the incidence of hypothyroidism caused by the treatment was 107 (35.8%) cases. The multiple regression analysis showed that the weight of thyroid, the maximum radioiodine uptake of thyroid, and the free triiodothyronine (FT3) level were major factors that influenced the effect of the ¹³¹I therapy (P<0.05). Conclusion The empirically calculated dose of ¹³¹I therapy for the treatment of Graves disease should take into account the effects of weight of thyroid, the maximum radioiodine uptake of thyroid, and the FT3 level on the therapy. The empirically calculated dose of ¹³¹I therapy is suitable for recurrent patients or patients with poor therapeutic effect for anti-thyroid drug or severe side effects.