Neurofibromatosis type 1 and ataxia telangiectasia are included in neurocutaneous syndrome. Ataxia telangiectasia is well known as the radiation hypersensitivity disease. The radiation sensitivity in neurofibromatosis type 1 is not well known. We report two cases of breast cancer with neurofibromatosis type 1. One patient received postoperative radiation therapy on left chest wall. The other patient received postoperative radiation therapy on right chest wall and supraclavicular area. We observed clinical radiosensitivity in these patients. Both patients did not show any acute adverse clinical response in chest wall and lung. Further evaluation of radiosensitivity in patients with neurofibromatosis type 1 is needed.