The malignant germ cell tumor found in the gonad can originate in the anterior mediastinum. Endodermal sinus tumor[Yolk sac tumor] is a kind of malignant germ cell tumor and is derived from extra-embryonic mesoderm. We experienced a case of primary mediastinal endodermal sinus tumor occurred in 22 year old male patient. His chief complaint was anterior chest pain for 2 days. The tumor located in the anterior mediastinum and invaded upper lobe of the deft lung and pericardium. A left upper lobe resection including phrenic nerve and pericardium was performed and the tumor in the anterior mediastinum was excised. The patient has been treated with combination chemotherapy[Cis-platinum, Vincristine, Actinomycin-D, & Cyclophosphamide} and followed up for 4 months with partial remission.