Mediastinoscopy is a diagnostic surgical method in thoracic diseases particularly in staging of lung cancers. Its morbidity and mortality levels are very low. Massive hemorrhage is the most common and mortal complication of mediastinoscopy. A 61 years old man with mediastinal mass had a massive hemorrhage during mediastinoscopy. A hearth-lung pump is prepared and emergent sternotomy is performed. Because of the innominate artery was found as ruptured, it was primarily repaired and bleeding was under controlled.