The most common neoplasms of the peritoneum are malignant mesothelioma and serous papillary adenocarcinoma. Clear cell carcinoma (CCC) is mostly derived from the ovary and often associated with endometriosis. We describe the clinicopathologic features of two cases diagnosed as CCC of the peritoneum origin. Case 1, a 53-year-old woman, presented with upper abdominal and pelvic tumors. Case 2, a 66-year-old woman, presented with massive ascites and abdominal tumor. The ovaries and uterine endometrium of these cases were not affected, and the tumors were diagnosed as Stage IIIc CCC of the peritoneum origin. Pathologically, endometriosis was not observed in either case. Adjuvant chemotherapy using irinotecan and cisplatin was effective in one case. The cases and a review of the literature suggested that residual tumor volume size determines the survival of these patients, and that the tumors show resistance to conventional platinum-based chemotherapy.