Objective. The authors describe a case of synovial sarcoma in the left mandible body. Study design. The primary tumor was investigated morphologically and immunohistochemically. The patient was treated with madibulectomy and lymph node dissection, which was followed by an immediate reconstruction of the left mandible with a revascularized osteomyocutaneous fibula free flap. Results. The primary tumor was described as gingival sarcoma. The initial preoperative biopsy showed positive staining for cytokeratin, vimentin, smooth muscle actin, and desmin by immunohistochemistry. The definitive diagnosis of monophasic synovial sarcoma was established following postoperative excision biopsy. Antigens of S-100 and CD99 displayed positive staining but epithelial membrane antigen, Bcl-2, and CD34 were negative. Also, no metastasis or other bone swelling was observed by radionuclide survey suggesting the left mandible was the primary lesion of occurrence. Conclusions. Synovial sarcoma is an uncommon soft tissue malignant neoplasm. This is the sixth case of primary synovial sarcoma occurring in the jaw.