Broncho-gastric fistula caused by benign gastric ulcer perforation after esophagectomy is very rare. In general anesthesia of a patient with broncho-gastric fistula, in spite of hyperventilation, leakage of the anesthetic gases through fistula may make the patient hypercapneic, and positive pressure ventilation may increase the risk of the pulmanary aspiration by the regurgitation of gastric fluid by stomach distension. For that reason, in this patient, denitrogenation was performed during patient's voluntary respiration with 100% oxygen for 5 minutes, and induction was performed without positive pressure ventilation, and one lung ventilation was carried out. Hypoxemia was followed by one lung ventilation because his pulmonary function was moderate obstructive type and his lung was damaged by aspiration of gastric fluid via broncho-gastric fistula. A low level of continuous positive airway pressure (CPAP) has no significant hemodynamic effect and can maintain the patency of nonventilated lung, so hypoxemia induced by one lung ventilation may be reduced. Thus we carried out one lung ventilation with CPAP (10 cmH2O) in nonventilated lung and blocked broncho-gastric fistula with a bronchial blocker for prevention of both regurgitation of gastric fluid and leakage of anesthetic gases. One lung anesthesia was performed without any problem in this case.