A bronchial blocker (BB) is preferred for lung separation in patients with difficult airways. However, BBs, unlike double-lumen tubes, must be placed in the bronchus of the lung being operated on, hence can be damaged by surgical manipulation. Intubation was unexpectedly difficult in this male patient, so a Coopdech BB was placed in the right mainstem bronchus through a single-lumen tracheoscopic ventilation tube for a thoracoscopic right upper lobectomy. During the bronchial resection, however, the distal tip of the BB was transected and pinched in the staple line, so the staple line was partially opened, and the BB was withdrawn into the trachea. The opened bronchial stump was sutured manually under apnea without conversion to an open thoracotomy, and there was no significant air leakage through the suture line. This case underlines the importance of frequently evaluating the position of a BB during lung surgery.