We report a case of primary malignant mesothelioma of the appendix. A 35-year-old man without any history of asbestos exposure was admitted to our hospital for further examination following the discovery of multiple liver tumors, an ileocecal tumor, and abdominal lymph node swelling. An ultrasound-guided liver tumor biopsy revealed malignant mesothelioma. Despite receiving systemic chemotherapy, he died 3 months after the initial diagnosis. At autopsy, a diagnosis of multiple organ metastases from a malignant biphasic mesothelioma of the appendix was made. To our knowledge, this is only the second reported case of primary malignant mesothelioma of the appendix.