An 11-month-old male mixed breed dog was euthanized due to two months history of vomiting and anorexia. At necropsy, numerous, multifocal or coalescing, firm, protruding nodules, 5 to 40 mm in diameter were scattered throughout the mesentery and omentum. Histologically and immunohistochemically, the nodules were diagnosed as malignant mesothelioma. Metastasis to the regional mesenteric, mediastinal and tracheobronchial lymph nodes were observed.