We report a case of multicystic mesothelioma in the visceral peritoneum anterior of the ascending colon. A 39-year-old female patient visited hospital with a palpabel tender mass in the right flank. An ultrasonogram showed multiple cystic mass lesions in the right flank and CT scan showed a multicystic rative mass with enhancing wall and septum in front of the ascending colon. The patient underwent explolaparotomy and the mass. which inpathology turned out to be a benign multicystic masothelioma, was removed.