Two of the common causes of hypercalcemia are malignancy and primary hyperparathyroidism. These disorders are easily diagnosed by the clinical manifestations and measurement of the serum intact parathyroid hormone (PTH) level. On the other hand, hyperthyroidism is an uncommon cause of hypercalcemia. The diagnosis of hypercalcemia associated with hyperthyroidism can only be made by excluding the common causes of hypercalcemia and by observing the improvement of the hypercalcemia and its associated symptoms with normalizing the thyroid function. Herein we reported our experience with a 67 year-old woman who presented with nausea and vomiting. She showed elevated serum calcium and phosphorus levels. Serum intact PTH level was 1.1 pg/mL (normal range; 10~65). The results of the thyroid function test were compatible with hyperthyroidism. After resolution of the thyrotoxicosis with combination treatment of methimazol and Lugol's solution, the patient's serum calcium and phosphorus levels were normalized and the symptoms were improved.