Background: Primary pericardial synovial sarcoma is an extremely rare malignant invasive tumor with dismal prognosis. Methods: We herein report a case of a 29-year-old woman of Chinese descent, who was admitted to our hospital with a fever and subsequently diagnosed to have primary pericardial synovial sarcoma. Results: A giant mass was found on transthoracic echocardiography. Computed tomography and magnetic resonance imaging identified a giant pericardial mass compressing the left atrium. Ultrasound-guided biopsy confirmed a monophasic synovial sarcoma. The patient refused further treatment and died 22 months later. Conclusion: We report a rare case of primary pericardial synovial sarcoma, which generally has a poor prognosis. Molecular genetic analysis may greatly contribute to the definite diagnosis.