Bladeless trocar decreases accidental injuries and incisional hernia; further a closure of fascial defect is considered to be unnecessary if a 12-mm bladeless trocar is used at nonmidline. We present a case of bowel herniation after using 12-mm bladeless trocar in robotic colorectal surgery. A 67-year-old woman had rectal cancer and underwent a robot-assisted low anterior resection. The facial defect after using 12-mm bladeless trocar was closed with the routine procedure. On postoperative day 7, her hernia of the trocar site was diagnosed by an abdominal computed tomography. The herniation was reduced with laparoscopic surgery. In conclusion, a trocar site hernia can occur after using a 12-mm bladeless trocar in robotic surgery.