A 58-year-old woman presenting with abdominal distension was diagnosed with a tumor in the right ovary. A chest-abdominal-pelvic computed tomography scan revealed multiple lung metastases, multiple liver metastases, and peritoneal dissemination. Invasion of the rectum by peritoneal dissemination of the Douglas' pouch was suspected. She was diagnosed with Stage Ⅳ right ovarian cancer and was treated with preoperative chemotherapy. After chemotherapy, debulking surgery of the abdominal cavity (total hysterectomy, bilateral salpingo-oophorectomy, partial omentectomy, and Hartmann's procedure) was performed. Because there was swelling observed in multiple mesorectal lymph nodes, lymph node dissection was performed based on methods used for rectal cancer surgery. Postoperative histopathological examination revealed multiple mesorectal lymph node metastases arising from ovarian cancer. We suggest that mesorectal lymph node dissection be considered a part of debulking surgery for ovarian cancers that have invaded the rectum.