Fat-forming solitary fibrous tumor(SFT) is generally slow-growing neoplasm and shows benign histology. Rarely, some fat-forming SFTs show malignant characteristics. An 87-year-old man visited our hospital complaining of dyspnea. 36months ago, he underwent wide excision for malignant SFT of thigh. The patient was followed postoperatively and there was no evidence of metastasis for 14month. But new mass was detected on right lung. It was metastasis of malignant fat forming SFTs. The patient died 1month after diagnosis. In this report, we describe, for the first time, a case of sudden isolated pulmonary metastasis from malignant fat-forming solitary fibrous tumor.