A 60-year-old woman presented at our hospital with abdominal pain and vomiting.Three abdominal tumors were detected, and she was referred to our department for surgery.She underwent an enterectomy including 2 of the tumors.The third tumor could not be resected because it had invaded the superior mesenteric artery(SMA)and superior mesenteric vein(SMV). Based on positive immunohistochemistry results for S-100 protein and desmin, nerve sheath differentiation with rhabdomyoblastic differentiation was confirmed, and she was diagnosed with a malignant triton tumor(MTT).She received postoperative chemotherapy with adriamycin and dacarbazine.However, she died 7 months after surgery, with multiple peritoneal metastases.MTT is a subtype of malignant peripheral nerve sheath tumor and is very rare.MTT has a poor prognosis with a high tendency of local recurrence and early metastasis.The most common treatment strategy is radical resection followed by postoperative chemoradiotherapy.When preoperative diagnosis is possible, radical resection with clear margins should be performed.