Osteosarcoma may rarely originate from the axial bones such as pelvis or vertebrae. In some pelvic and most vertebral primary tumors, resection often is not possible completely. In general, these tumors cannot be resected with negative margins so they need additional radiotherapy and chemotherapy, but results are unfavourable because of poor local control and high incidence of distant metastases. This is a case report of sacral osteosarcoma which was treated successfully with chemotherapy and radiation therapy. The patient is a 14-year-old boy with a large osteosarcoma tumor in the first sacral vertebral body, with extra skeletal extension. The patient took radiotherapy (6000 centigray) plus chemotherapy regimen consisting of doxorubicin and cisplatin. In the last follow up 48 months later, the patient was completely asymptomatic with normal performance and there was not any evidence of local progression or distant metastasis.