There has existed controversies concerning the relationship between hypokalemia and perioperative dysrhythmia. Definite lowest serum potassium level that guarantee safety has not been determined. We found accidentally severe hypokalemia (below than 2 mmol/L) after the induction of anesthesia in a 51-year-old man who had no systemic disease. This patient suffered from a traffic accident 18 years ago and has bed-ridden up to now. In addition, recently he had poor oral intake. The patient's serum potassium level was within normal range in blood chemistry taken 5 days before operation. Although no dysrhythmia developed, we administered potassium during operation. With the continuous potassium and magnesium replacement postoperatively, the serum potassium level returned to normal range. With the experience of this case, we had a chance to review the effect of hypokalemia on dysrhythmia and causes of hypokalemia.