The aorta is the most common major thoracic artery injured by blunt chest trauma. Injuries to major aortic arch branch arteries can also occur but are much less common than aortic injuries in the setting of blunt trauma. Although internal mammary artery (IMA) injury is uncommon and rarely diagnosed in cases of blunt chest trauma, it is one of the important sources of bleeding in chest trauma. IMA bleeding can cause ongoing blood loss and may lead to serious conditions such as extensive hemothorax, anterior mediastinal hematoma or its catastrophic complication, cardiac tamponade. However such arotic and branch artery injuries are not easily detected by plain radiograph, and are detected indirectly because of associated mediastinal hematoma. Herein, we report a case of IMA injury caused by blunt chest trauma secondary to pedestrian traffic accident. The injured patient was successfully treated by transcatheter arterial embolization (TAE). (J Trauma Inj 2012;25:296-299)