We present a case of Mobitz type II atrioventricular block during one-lung ventilation in a 74-year-old man with lung cancer under anesthesia. Premedication with atropine 0.5 mg and midazolam 2 mg intramuscularly were given 30 min before entering the operating room. Before anesthesia, his heart rate was 72 beats x min(-1) with normal sinus rhythm and blood pressure was 120/70 mmHg. An epidural catheter was placed at T4-5 interspace and 1.5% mepivacaine was infused (7 ml bolus and 5 ml x hr(-1) thereafter). After placing external pacemaker paddle, general anesthesia was induced with propofol 3 microg x ml(-1) and fentanyl 0.1 mg, and tracheal intubation was facilitated with vecuronium 6 mg. Anesthesia was maintained with propofol and fentanyl. After initiating one-lung ventilation, the patient developed Mobitz type II block with a heart rate of 30 beats x min(-1). External pacing was started (rate: 80 beats x min(-1), output: 150 mA). However, body movement associated with external pacing interrupted operative procedure, and blood pressure was not restored effectively. Therefore, external pacing was stopped and atropine and dopamine were administered. Mobitz type II block continued, but blood pressure and heart rate were maintained during the operation. Cardiac rhythm was restored the next morning without any treatment. Propofol, fentanyl, and thoracic epidural anesthesia could caused Mobitz type II block. External pacing should not be used for thoracic surgeries.