BACKGROUND Endometrial stromal tumors originate from the endometrial stroma and account for < 2% of all uterine tumors. Uterine tumor resembling an ovarian sex cord tumor (UTROSCT) is a rare histological class of endometrial stromal and related tumors according to the latest World Health Organization classification of female genital tumors. Here, we report a case of UTROSCT in a 51-year-old woman. CASE SUMMARY A 51-year-old woman had irregular menses for 6 mo. The patient visited a local hospital for vaginal bleeding. Pelvic computed tomography (CT) showed a mass in the pelvic cavity. Five days later, she came to our hospital for further diagnosis. The results of contrast-enhanced CT and pelvic ultrasound at our hospital suggested a malignant pelvic tumor. She then underwent total removal of the uterus with bilateral salpingectomy. Postoperative histological examination showed that the tumor cells had abundant cytoplasm, ovoid and spindle-shaped nuclei, fine chromatin, a high nucleoplasm ratio, and a lamellar distribution. The findings were consistent with UTROSCT, and the results of immunohistochemical analysis supported that diagnosis. The tumor was International Federation of Gynecology and Obstetrics stage IB. No adjuvant therapy was administered after radical surgery. The patient was followed up for 58 mo, and no recurrence was found. CONCLUSION We report a case of UTROSCT with abnormal menstruation as a symptom, which is one of the most common symptoms. In patients with vaginal bleeding, ultrasonography can be used as a screening test because of its convenience, speed, and lack of radiation exposure. For patients with long-term tamoxifen use, routine monitoring of the endometrium is recommended. As UTROSCT may have low malignant potential, surgery remains the primary management strategy. Additionally, fertility preservation in patients of childbearing age is a vital consideration.