We report on two cases of primary ovarian fibrosarcoma detected in two women aged 44 and 34 years old. In the first case, an 18 x 17 x 10 cm multilobular tumor was detected in the left ovary. In the second case, a 13 x 9 x 3 cm and a 7 x 6 x 2 cm tumor were found in the left and right ovaries, respectively. In addition, a large quantity of ascitic fluid was detected. In both cases, a total hysterectomy with bilateral adnexectomy and an omentectomy were performed. No evidence of lymph-node enlargement was detected in either case. Microscopic findings demonstrated densely, cellular spindle-shaped tumor cells with increased mitotic activity (17 and 8/10 high-power fields, respectively). Immunohistochemical analyses showed that tumor cells were positive for vimentin and negative for smooth muscle actin, S-100, and estrogen receptor. Progesterone receptor was positive only in the second case. After surgery, both patients received several courses of combination chemotherapy. Neither patient demonstrated any evidence of disease recurrence during follow-up for 10 years and 5 years, respectively.