Peritoneal mesothelioma is an unusual disease which diffusely involves the peritoneal surface. The incidence is approximately one per 1,000,000, and one fifth to one third of all mesothelioma are peritoneal in origin. Asbestos exposure is linked to the development of peritoneal mesothelioma as a significant etiology, but further investigation should be conducted. Abdominal sonography, abdominal CT and cytologic examination of ascitic fluid are used to confirm the diagnosis, but rarely provides proper diagnosis. Laparoscopy with biopsy is the most common diagnostic method for definite diagnosis of mesothelioma. Cytoreductive surgery and intraperitoneal chemotherapy have been suggested for better survival since the median survival after the initial diagnosis is near to 50 months. This report describes a case of 73-years-old male patient presented with abdominal pain and distension. This patient had not been exposed to asbestos. Abdominal sonography and CT showed massive ascites, multiple omental masses and peritoneal thickening. It was difficult to distinguish peritoneal mesothelioma from carcinomatosis. Laparoscopy and peritoneal biopsy was conducted and immunostaining examination confirmed the diagnosis of peritoneal mesothelioma.