Solitary fibrous tumor of retroperitoneum is very rare with unpredictable behavior. We present a case of a 67-year-old male with large pelvic, abdominal mass measuring 20x13x7 cm and weighing 2.8 kg. Needle biopsy showed malignant spindle cell tumor. The mass was resected. The hypoglycemia and lower limb edema were resolved completely after surgery.