An ovarian serous cystic tumor of low malignant potential with solid mural sarcoma-like nodules is reported. This tumor metastasized to the ileal wall. The nodules in the ovary and in the ileal wall were made up of highly malignant cells with admixed osteoclast-like multinucleate giant cells. Immunohistochemical reactions demonstrated the epithelial differentiation of the tumor. We propose that the term "sarcomatoid carcinoma" of the ovary should be adopted for these lesions.