Malignant peritoneal mesothelioma is a rare disease, not previously reported in Taiwan. The reported case concerns a 64-year-old veteran who had suffered from abdominal pain and distension for several days. After exploratory laparotomy, segmental resection of the small intestine, excised a mesenteric mass. A characteristic biphasic pattern resulting from the admixture of gland-like area and a sarcomatous stroma presented in the histologic section. A series of histochemical, immunohistochemical and ultrastructural studies proved this to be a malignant peritoneal mesothelioma. The patient died after a course of post-operative chemotherapy. History of asbestos exposure, with which the tumor is usually intimately associated, could not be traced with certainty. Poor prognosis is the rule of the disease; almost all patients die within two years of diagnosis. An effective therapeutic modality is still unavailable. Here the clinical and pathologic characteristics of the tumor are described, with a brief review and discussion of the pathogenesis as well as the obscured therapeutic problem.