We report the case of a 69-year-old woman who presented with postmenopausal bleeding. Endometrial curettings showed complex atypical hyperplasia with focal well-differentiated adenocarcinoma. A computed tomographic scan of the abdomen revealed a right ovarian mass. Histologically, the right ovarian tumor was a fibrothecoma with minor sex cord elements showing focal fibrosarcomatous change. Fibrosarcoma of the ovary is a rare tumor that is considered to arise de novo or secondary to benign fibromatous tumors. Fibrothecoma of the ovary with minor sex cord elements is also a rare entity. To the best of our knowledge, this is the first reported case of a fibrosarcoma arising in a fibrothecoma with minor sex cord elements.