We report a case of early intrathoracic migration of Kirshner wire (K-wire), which had been-used for fixation of proximal humerus fracture. A 74 year-old-woman visited the emergency room due to sudden onset of dyspnea. A chest x-ray and CT scan taken at the emergency room demonstrated 3 K-wires that had been applied to the proximal humerus fracture, 1 K-wire in the anterior chest wall, and mild pneumothorax of the right lung. An emergency removal of K-wire using thoracoscopy was performed and a chest tube was inserted for the treatment of pneumothorax during thoracic surgery. We removed residual 3 K-wires from the right proximal humerus and fixed right proximal humerus fracture by open reduction and internal fixation using a proximal humerus locking plate. We think that if a proximal humerus fracture is fixed using smooth K-wire, patients require close follow-up with the use of x-ray until the K-wire has been removed, in addition, it is very important to take steps to prevent K-wire migration.