Difficulties in ventilation are sometimes encountered in intubated patients. In these cases, endotracheal tube kinking, or an obstruction by secretion or foreign bodies should be considered. We experienced an endotracheal tube obstruction by a foreign body. The patient was a 36 year old woman who had a traffic accident. She had already been intubated when entering operating room. However, ventilation was difficult, which was presumed to be caused by an endotracheal tube obstruction. The endotracheal tube was examined by fiberoptic bronchoscopy and the patient's broken tooth was found inside the endotracheal tube. The endotracheal tube was exchanged and ventilation was normalized.