Synovial sarcoma is a rare malignant neoplasm that develops most frequently in the extremities. A 68-year-old man presented with a painful mass on the right side of his chest with a 10-year history. Gross findings revealed a mass beneath the pectoralis major muscle. The pathologic findings showed the tumor was predominantly composed of spindle cells the arranged in compact interdigitating fascicles and scattered epithelial nests were seen. A diagnosis of synovial sarcoma was made.