A rare case of Ewing's sarcoma of the mandible is reported. A 50-year-old man was referred to our hospital because of right mandibular swelling and spontaneous pain. A biopsy specimen obtained by his dentist strongly suggested small round cell osteosarcoma. Since the tumor rapidly grew while preparing for chemotherapy, hemimandiblectomy and radical neck dissection were carried out with the patient under general anesthesia. Finally, a histopathological diagnosis of Ewing's sarcoma was made on examination of the surgical specimen. The patient was treated with adjuvant local irradiation (50Gy) and combination chemotherapy (VAIA, T-16). Although the primary lesion was well controlled, the patient died of multiple bone metastases 6 months later after the operation.