Solitary fibrous tumor (SFT) is a rare spindle cell neoplasm that is benign in most cases. Although SFT was first recognized to arise only in the pleura, recent reports indicate that SFT can involve a wide range of anatomical sites. To date, 17 cases of pelvic SFT have been reported. Herein is reported a case of a 74-year-old woman with a giant malignant SFT in the pelvis. Along with massive invasion to adjacent organs and multiple lung metastases detected on radiography, biopsy from the tumor through the vaginal wall showed malignant looking spindle-cell neoplasm with increased cellularity, areas of necrosis, and high mitotic activity (5/10 high-power fields). Immunohistochemically, the tumor cells were diffusely and strongly positive for CD34, CD99, and bcl-2. Based on pathological features and clinical presentation, diagnosis of malignant SFT was made. The patient received systemic and the intra-arterial chemotherapy followed by whole pelvic radiation therapy (50 Gy). Initial chemotherapies failed to control the tumor. Afterwards, improvement was observed radiologically and pathologically in the 12 months' follow up after the radiation therapy. This is the first report related to therapeutic remarks on advanced malignant SFT.