We report a case of peritoneal mesothelioma presenting with bilateral hydronephrosis, which was difficult to be diagnosed. A 43-year-old woman was admitted to our hospital with acute renal failure. Ultrasonography revealed bilateral hydronephrosis. Retrograde pyelography revealed the stenosis of bilateral lower ureter. Pelvic magnetic resonance imaging demonstrated only a small mass lesion around the bilateral ureter. Other examinations showed no findings of malignancy. Under the diagnosis of retroperitoneal fibrosis, steroid therapy was performed. After 3 months, computed tomography (CT) revealed multiple abdominal masses. Percutaneous needle biopsy of tumor was performed. Pathological diagnosis was peritoneal mesothelioma. Chemotherapy based on the pleural mesothelioma was done but not effective, she died 9 months after the first medical examination.