We experienced a case of severe intraoperative hyperkalemia during laparoscopic radical nephrectomy in a 60-year-old male patient with renal insufficiency, whose hypertension had been managed by preoperative angiotensin II receptor blocker (ARB) and adrenergic beta-antagonist. After renal vessel ligation, his intraoperative potassium concentration suddenly increased to 7.0 mEq/L, but his electrocardiography (ECG) did not show any significant change. While preoperative ARB therapy has been regarded as a contributing factor for further aggravation of underlying renal insufficiency, we assumed that nephrectomy itself and rhabdomyolysis caused by surgical trauma also aggravated the underlying renal dysfunction and resulted in sudden hyperkalemia. Hyperkalemia was managed successfully with calcium gluconate, insulin, furosemide and crystalloid loading during the intraoperative and immediate postoperative periods, and potassium concentration decreased to 5.0 mEq/L at 8 hours after the operation. The patient's hospital course was uncomplicated, but his renal function deteriorated further.