Schwannoma is a tumor that usually originates soft tissue peripheral nerves. Primary mesenteric schwannomas are rare, and furthermore, there are few reports of this with secondary ossification, which is extremely rare. Herein we report a case of primary mesenteric schwannoma with secondary ossification in a 46-year-old Japanese woman with recurrent postprandial abdominal pain and weight loss. Her vital signs were stable, and her blood test was almost normal except for a slight elevation of CA125. Computed tomography revealed a whirl sign indicative of superior mesenteric torsion. In contiguity with a constricted portion of the intestine, an approximately 70-mm, well-circumscribed tumor with calcifications, which was fed by the superior mesenteric artery was visible. On magnetic resonance imaging, the tumor appeared hypointense on T1-weighted images and inhomogeneous hyperintense on T2-weighted images. As a gastrointestinal mesenchymal tumor was suspected, we performed partial small intestinal resection including the tumor. Intraoperatively, the tumor was found to be incarcerated into a hernial orifice created by the adhesion of the sigmoid colon with the abdominal wall and uterus. Pathologically, the tumor had no continuity with the intestinal wall. It mainly consisted of hypocellular mucous, and spindle-shaped cells were sparsely distributed. Some areas were hypercellular with palisading arrangement cells. This was suggestive of an Antoni B>Antoni A type schwannoma. It also included secondary ossification and blood vessel assembly. The patient has had an uneventful postoperative course without recurrence for about 17 months. Primary mesenteric schwannoma is rare, and to our knowledge, only 20 cases including this case have been reported. Moreover, there has only been one report of primary mesenteric ossified schwannoma in 2018, and there has been no report in Japan so far. We report our experience with the successful treatment of primary mesenteric ossified schwannoma and review the literature.