Cystic mesothelioma of the peritoneum is a rare benign neoplasm that occurs predominantly in young to middle-aged women and tends to recur locally. Pelvic viscera is the most common predilection site of cystic mesothelioma. Authors report a case of multicystic mesothelioma of the pelvic pelvic peritoneum. The pelvic ultrasonography showed a large, confluent, and thin-walled multilocular cystic mass occupying the pelvic cavity and lower abdomen. The cystic mass was flattened and elongated. Each cyst of variable size was separated by thin septa and filled with translucent fluid. Cystic mesothelioma should be included in the differential diagnosis of the cystic peritoneal masses, especially in reproductive-aged women.