Pleural metastasis of synovial sarcoma that originally developed in the soft tissue is a very rare entity. We report here the detailed clinical features of such a case. An asymptomatic 25-year-old female, with a history of a resected synovial sarcoma in her left brachial muscle and pulmonary metastasectomy of the right lung, presented a small nodule in the periphery of the left lung on a routine chest-computed tomography. Exploratory thoracoscopy was then performed. A soft flat red tumor approximately 2 cm in diameter was shown on the pleura of the lingula, mimicking a blood clot on the pleura. The tumor was removed by partial resection of the lung. The mass lay in the pleura and did not seem to invade the lung parenchyma macroscopically. Intraoperative frozen sectioning evidenced metastatic synovial sarcoma. Many small patchy red lesions were also found on the visceral pleura of the lung and parietal pleura of the diaphragm. We diagnosed unresectable pleural metastases of synovial sarcoma and finished the operation after sampling another pulmonary pleural lesion. The patient then underwent ifomide-based chemotherapy and survived for 3 years after her initial surgery. Postoperative histopathological examination revealed a solid and bundle-like proliferation of a short spindle cell tumor with a monophasic pattern, which was diagnosed as a metastatic pleural synovial sarcoma. A hemangio-pericytomatous pattern was also seen; therefore the lesion looked like a blood clot because of its rich vascularity.