We reported a rare synovial sarcoma arising within sacrum of a 12-year-old boy. A plain radiograph, magnetic resonance imaging performed before surgery, and the intraoperative findings showed that the tumor was S2 and below. Immunohistochemically, desmin and CD34 were negative. CK, CK7, CK1, CK3, CK8, CK19, Bcl-2, E-cadherin, ki-67, P53, SMA, CD99, CD56, S-100, vimentin, and epithelial membrane antigen were positive. Some were focal positively reactive to S-100, P53, and ki-67. The spindle cells were strongly positive for vimentin and CK3. The immunohistochemical findings confirmed its diagnosis of synovial sarcoma.