Introduction: Malignant peripheral nerve sheath tumor (MPNST) is a rare soft tissue malignancy and many of this tumor arise in the patients with neurofibromatosis (NF) type 1, with very poor prognosis. MPNST can arise anywhere of the body including head and neck or extremities, but intrathoracic MPNST is uncommon. We experienced a case of intrathoracic MPNST in a girl with NF type 1. Case Report: A 16-year-old girl visited our hospital, because of progressive chest discomfort and respiratory difficulty from 1 month prior to visit. She had multiple café-au-lait spots and cutaneous neurofibromas, indicating NF type 1. Her computed tomography image of chest revealed a large mass (20×18×12 cm) occupying the right thoracic cavity, with multiple pleural and pulmonary nodules suggesting metastasis. She underwent immediate surgery (total resection of the intrathoracic tumor with chest wall reconstruction). Microscopic finding of the tumor showed a spindle-shaped cells with pale, eosinophilic cytoplasm. Immnohistochemically, many tumor cells expressed neuron-specific enolase, CD68 (focal), but not desmin, CD34, S100, and smooth muscle actin, which were consistent with MPNST. After surgery, she had 6,600 cGy of radiotherapy to right whole lung field and pleura since postoperative day 40. Subsequently, she started to receive the 6 courses of chemotherapy consisted of vincristine, adriamycin, and cyclophosphamide, alternating with ifosfamide and etoposide. However, her residual metastatic pleural and pulmonary tumors showed no definite response to radiotherapy and chemotherapy, and they showed rapid progression with newly appeared pulmonary nodules. She showed a large amount of malignant pericardial effusion during chemotherapy. In spite of pericardiocentesis and supportive cares for effusion, her effusion did not decreased, and finally she died of progressive of disease at 9 months after surgery. Conclusion: The authors report a case of intrathoracic MPNST in a 16-year-old girl with NF type 1. Despite its rarity, MPNST should be considered as a differential diagnosis of intrathoracic mass in children with NF type 1.