Primary ovarian leiomyosarcoma (LMS) is very rare, with only 72 cases reported. Its behavior is aggressive, and there is no standard therapy. A 62-year-old woman with a giant pelvic tumor underwent CT and MRI. An irregular, 30-cm, solid tumor that was suspected to be malignant was seen. On laparotomy, the tumor was derived from her right ovary and adhered widely to the retroperitoneum. On pathological examination, it was an ovarian leiomyosarcoma. Adjuvant chemotherapy (docetaxel and gemcitabine) was given. Three months after surgery, CT showed multiple liver metastases. Pazopanib, ifosfamide, doxorubicin, and eribulin were given with no effect, and the woman died 18 months after the primary operation. With the administration of pazopanib, proteinuria of 2.3 g/dl occurred, which made continuous administration impossible. Since ovarian LMS may not respond to chemotherapy for other soft tissue sarcomas, study of more ovarian LMS cases is needed.