We report here on an unusual case of mucinous cystic tumor that was associated with endometriosis in the cecum. A 45-year-old woman was admitted to the hospital due to her 5 day history of right lower quadrant abdominal pain with a mild fever. A laparotomy was performed under the clinical impression of the tubo-ovarian abscess. A relatively well defined a multi-locular cystic mass (8.0x8.0x7.0 cm) filled with white-to-yellow thick mucoid material was found in the wall of the cecum. The right ovary and fallopian tube showed marked fibrous adhesion to the external surface of the cecal mass. A right hemicolectomy and salpingo-oophorectomy were performed. Histologically, the tumor was similar to those of ovarian borderline mucinous tumor, the intestinal type, and the mucinous epithelium of the tumor was merged with the endometriotic epithelium and stroma. On immunostaining, the CK20 positive mucinous epithelium was well demarcated from the CK7 endometriotic epithelium. This is the first case of low-grade mucinous cystic tumor intimately associated with intestinal endometriosis in the cecum.