The mixed mesodermal tumor is a very uncommon malignancy. The aggressiveness of this lesion is illustrated by extremely poor prospects for afflicted patients: postoperative survival is usually shorter than 24 months. According to the literature, malignant mixed tumor of the ovary is rather rare and its occurrence with other malignancy is exceptional. We report here a case of a 62-years old woman with serous cystadenocarcinoma in the right ovary and a heterologous malignant mixed mesodermal tumor in the left one. Both tumors expressed cytokeratins, while only the mesodermal tumor expressed S-100 and focal NSE.