Prolonged oversedation occurs frequently in postoperative care units, and sometimes delays transfer to normal units. Flumazenil is a known reversal drug for benzodiazepines, and is used to reverse the oversedation caused by benzodiazepines. However, we found that flumazenil was effective in a case of sevoflurane induced oversedation. A prolonged oversedation of 90 minutes occurred after sevoflurane anesthesia without benzodiazepine at a postoperative care unit. Immediately after an intravenous injection of flumazenil, the patient fully awoke and was oriented.