An endotracheal tube obstruction causes serious complications, including cardiovascular instability, pneumothorax, pulmonary edema and brain death. A 74 year old woman was scheduled to undergo a laminectomy and instrument fixation due to tuberculosis spondylitis. The patient was intubated with a 7.0 mm reinforced endotracheal tube, and moved into the prone position. At 100 min after the initiation of anesthesia, signs of partial endotracheal obstruction were observed, including high airway pressure and low tidal volume. The signs of an airway obstruction were aggravated as the operation proceeded. Thirty minutes after the sign of a partial obstruction, those of a total endotracheal obstruction were observed. A mucoid impaction in the endotracheal tube was detected using flexible fiberoptic bronchoscopy. After removing this plug, the ventilation of the patient was maintained within normal limits.