Thyroid cancer and Graves’ disease may present simultaneously in one patient. The incidence of the development of hyperthyroidism from metastatic differentiated thyroid carcinoma is rare. We herein report a case of metastatic follicular carcinoma complicated with Graves’ disease after total thyroidectomy. A 57-year-old woman underwent right hemithyroidectomy for follicular carcinoma. Metastatic lesions appeared in the lungs and skull two years after the first surgery, and remnant thyroidectomy was performed for radioactive iodine-131 (RAI) therapy, during which the TSH receptor antibody (TRAb) was found to be negative. The patient was treated with RAI therapy four times for four years and was receiving levothyroxine suppressive therapy. Although radioiodine uptake was observed in the lesions after the fourth course of RAI therapy, metastatic lesions had progressed. Four years after the second surgery, she had heart palpitations and tremors. Laboratory data revealed hyperthyroidism and positive TRAb. She was diagnosed with Graves’ disease and received a fifth course of RAI therapy. 131I scintigraphy after RAI therapy showed strong radioiodine uptake in the metastatic lesions. As a result, the sizes and numbers of metastatic lesions decreased, and thyroid function improved. Metastatic lesions produced thyroid hormone and caused hyperthyroidism. RAI therapy was effective for Graves’ disease and thyroid carcinoma.