Hemoptysis is described in many disease processes. However, a mediastinal teratoma is rarely considered in a patient presenting with hemoptysis. Since the mediastinal teratoma has no specific symptoms, its definite diagnosis is difficult before surgical intervention. Chest computed tomography is an important medium in evaluating mediastinal lesions. Bronchoscopy may be helpful in cases of a mediastinal teratoma with pulmonary involvement of the bronchial trees. We report herein a case of hemoptysis caused by a mediastinal teratoma with pulmonary involvement.