A solitary fibrous tumor (STF) is a relatively unusual neoplasm first described as a distinctive tumor arising from pleura. Some reports have shown that STF also affect extrathoracic regions. A 70-year-old woman was referred to our hospital for surgical treatment of an incidentally discovered thigh mass. We performed complete removal of the tumor. It was a soft tissue tumor with muscle indentation but without invasion to the surrounding muscles. The resected specimen was 7.0×6.3×5.2 cm. Histologically, the tumor was composed of a haphazard proliferation of spindle cells and epitheloid cells with hypercellularity and high mitotic activity. Immunohistochemistry showed positive immunoreactivity for CD34, CD99, bcl-2 protein, CD117, vimentin, smooth muscle actin and epithelial membrane antigen. We report, herein, on a rare case of malignant SFT in the thigh region along with a review of the literature.