Persistent descending mesocolon(PDM)is caused by absence of fusion of the descending colon to the retroperitoneum. A 67-year-old man with bloody stools was diagnosed with rectal cancer on colonoscopy. A computed tomography showed a medial displacement of his descending colon. The preoperative clinical diagnosis was rectal cancer with PDM, and robot assisted low anterior resection was performed. We found that the left-sided colon was shifted to the midline and adhered the cecum and the mesentery of small intestine. Robot assisted surgery enables surgery with the precise adhesiotomy in a stable field. PDM is a relatively rare anatomic abnormality. Character of PDM is adhesion between the left-sided colon and other organs and radially branch from the inferior mesenteric artery. It is important to understand the anatomical characteristics of PDM and to improve on existing surgical procedures to ensure safe robot assisted surgery these patients.