A 20 years old male patient was transferred to the operating room for mandibulo-maxillary reconstruction. We planned general anesthesia with nasotracheal intubation. Reinforced endotracheal tube was inserted through right nasal os and progressed to the epiglottic region. But the first trial was not successful because of the profuse bleeding from the nasal cavity. After suctioning, the second trial through the same route was successful. But at the time of skin incision, we found the lips of the patient were becoming pale, the SpO2 was falling down to lower than 70%. We found the patients left chest wall was motionless. The chest A-P film showed total atelectasis of the left lung. When a large blood clot was removed by the flexible bronchoscopy, the chest wall started to move well and the SpO2 came up to 99%. The following chest A-P film confirmed the resolution of the atelectasis.