A 29-year-old woman with a long-term history of Graves' disease was admitted for thyroidectomy. Torsade de pointes occurred after the subtotal thyroidectomy. The level of her serum calcium was lower than normal. After administration of calcium gluconate intravenously, torsade de pointes disappeared and was no longer recorded. It is assumed that her torsade de pointes was caused by hypocalcemia as a complication of subtotal thyroidectomy.