A 61-year-old woman was referred to our hospital with the complaint of severe dysphagia. Upper gastrointestinal endoscopy revealed an elevated tumor with an irregular surface located in the upper third of the stomach, and malignant melanoma was confirmed by biopsy specimens. Abdominal CT scan findings revealed that the tumor was invading the lateral segment of the liver and crus of the diaphragm. Total gastrectomy was combined with resection of the lateral segment of the liver and the crus of the diaphragm, and D2 lymphadenectomy and reconstruction by the Roux-en-Y method were carried out. Because of positive peritoneal washing cytology, monotherapy with dacarbazine, and combination therapy, including dacarbazine, nimustine hydrochloride, cisplatin, and tamoxifen citrate, were administered for treating the residual tumor. The patient died from peritoneal relapse 146 days after the initial surgery. Primary malignant melanoma arising from the stomach is reported as an extremely rare disease with a poor prognosis. In our case, multidisciplinary treatment including surgery and chemotherapy was insufficient to achieve long-term survival in a highly advanced malignant melanoma arising from the stomach.