The process of radioactive iodine treatment for hyperthyroidism is divided into three stages: First, the preparation work before treatment, the patient must first stop the anti-thyroid medication, so that the thyroid hormone level reaches a relatively high state, and the radioactive iodine is fully taken into the thyroid gland. Secondly, before the iodine-131 treatment, thyroid imaging and thyroid iodine uptake rate should be checked. Thirdly, after taking Iodine-131 treatment, the thyroid hormone level will start to decrease in about 1 month, and will reach its peak in 3 months, when most of the patients’ hyperthyroidism symptoms will be relieved significantly and the thyroid level will have reached normal. In the later stage, patients should also review the changes in thyroid function regularly, as some patients may develop hypothyroidism.