A rare uterine tumor showing sex-cord-like differentiation and marked osteoid metaplasia was found in a 33-year-old female. The tumor, occupying the uterine fundus, was multilobular, fleshy, and yellowish white, with punctations and poorly defined tumor margins into the subserosa. The tumor nodules were mostly composed of small, round, rather regular neoplastic cells with scanty cytoplasm and prominent nuclei. Epithelioid neoplastic cells with striking ovarian sex-cord-like arrangement, surrounded by fibrous tissue, were noticed. Polygonal neoplastic cells with marked osteoid metaplasia were also detected. The authors introduce an infrequent variant of uterine tumor resembling ovarian sex-cord tumor with osteoid metaplasia, probably of endometrial stromal cell origin. Because of deep myometrial infiltration without vascular invasion, malignant potential is considered. The patient is now alive without evidence of local recurrence or distant metastasis after abdominal total hysterectomy. ACTA PATHOL. JPN. 36: 1391–1395, 1986.