In this report, we present a rare case of Ewing's sarcoma with a peripheral primitive neuroectodermal tumor (ES/pPNET) arising from the abdominal cavity in a 20-year-old woman. The patient complained of upper abdominal pain. Radiological imaging showed a 15-cm mass penetrating to the proxymal jejunum in the upper abdominal cavity and peritoneal disseminations. Immunohistochemical studies revealed that the tumor was ES/pPNET. Although the patient underwent radiation therapy, she died of the disease two months after diagnosis. ES/pPNET in the abdominal cavity is extremely rare and our case showed aggressive behavior and an unfortunate outcome.