Sclerosing stromal tumor of the ovary (SSTO) is a rare benign neoplasm of the ovary, accounting for about 6% of all sex cord stromal ovarian tumors. Only 17 cases of SSTO occurring during pregnancy have been reported to date. We report a case of SSTO occurring during pregnancy and review the existing literature. A 32-year-old pregnant woman was found to have a 10-cm solid mass in the right adnexa, and a large volume of ascites fluid was detected by ultrasound examination in the second trimester. The patient underwent abdominal puncture to relieve her symptoms in the second trimester, and a partial right oophorectomy and cesarean section were performed at 39 weeks of gestation. Final pathology confirmed the diagnosis of SSTO. Both the mother and baby were well at 6 months of postpartum follow-up. Clinical symptoms, and hormone and imaging examinations are all helpful in making a differential diagnosis of SSTO, but the unique histopathological and immunohistochemistry findings remain the main diagnostic features. Pregnant women with SSTO usually undergo enucleation or unilateral oophorectomy, which generally does not have adverse pregnancy outcomes.