Acute airway obstruction during endotracheal anesthesia is embarrassing and critical situation which requires early diagnosis and immediate management. The authors experienced extremely high inspiratory resistance and declared expiration time during endotracheal anesthesia for right pneumonectemy of lung cancer in the left decubitus position. A foreign material was suspected to be dislodged in the trachea distal to the endotrac-heal tube. But the surgical procedure did not allow to change the tube for examination. Ventilation was managed by rotating and moving the endotracheal tube frequently. After extubation, the patient expectorated a polypoid mass and the cause of the obstru-ction was proved to be a result of the detached and dislodged tumor mass of the lung, in diameter 3X1.5 cm.