Malignant germ cell tumors which have the same morphological appearance as germinal tumor of the gonad are sometimes found in the anterior mediastinum. Pure endodermal sinus tumor among them is very rare. It is highly malignant and usually extensively invasive at the time of surgical consideration. The prognosis is poor, but improvements in systemic chemotherapy regimens may improved the outlook. A case of primary endodermal sinus tumor of the mediastinum was presented. He was a 23-year-old male with anterior chest pain, tenderness and exertional dyspnea for 1 month. The tumor was well encapsulated and adhered to pericardium. The microscopic appearance was indistinguishable from that of the analogous gonadal neoplasm. The patient has treated with combination of surgery and radiotherapy as daily 180 rad for 6 weeks schedule, and then has follow up about 3 months with early recurrence.