Primary pericardial synovial sarcoma is a rare disease. We herein report a case of synovial sarcoma that originated in the epicardium. A 13-year-old male visited our hospital with a fever and chest pain. Copious pericardial effusion and a large intrapericardial tumor were detected. An open-chest tumor resection was performed. A solid nodular tumor was observed in the pericardial cavity. The tumor was a polypoid mass that was pedunculated and grew from the inner surface of the pericardium near the origin of the SVC and ascending aorta. Histologically, the tumor cells were uniformly spindle shaped, with an ovoid or oval nucleus, and formed solid, compact sheets and fascicles. A storiform pattern was also observed. Based on the histopathological and immunohistochemical findings, and the fluorescence in situ hybridization detection of rearrangement of the SYT gene, a monophasic synovial sarcoma was diagnosed. We discuss the diagnosis and treatment of this case and review the pertinent literature.