BACKGROUND: Colorectal anastomosis using the double stapling technique (DST) has become a standard procedure. However, DST is difficult to perform in patients with anal stenosis because a circular stapler cannot be inserted into the rectum through the anus. Thus, an alternative procedure is required for colorectal anastomosis. CASE PRESENTATION: A 78-year-old woman presented with bloody stool. Colonoscopy and computed tomography revealed advanced low rectal cancer without lymph node or distant metastasis. We initially planned to perform low anterior resection using a double stapling technique or transanal hand-sewn anastomosis, but this would have been too difficult due to anal stenosis and fibrosis caused by a Milligan-Morgan hemorrhoidectomy performed 20 years earlier. The patient had never experienced defecation problems and declined a stoma. Therefore, we inserted an anvil into the rectal stump and fixed it robotically with a purse-string suture followed by insertion of the shaft of the circular stapler from the sigmoidal side. In this way, side-to-end anastomosis was accomplished laparoscopically. The distance from the anus to the anastomosis was 5 cm. The patient was discharged with no anastomotic leakage. Robotic assistance proved extremely useful for low anterior resection with side-to-end anastomosis. CONCLUSION: Performing side-to-end anastomosis with robotic assistance was extremely useful in this patient with rectal cancer and anal stenosis.