A 73-year-old woman underwent 2 surgeries for left breast cancer and its recurrence. Eighteen years after the first surgery for breast cancer, a colonoscopy was performed due to the presence of blood in her stool. A type 2 lesion was diagnosed in the ascending colon, which was revealed to be a group 5 tumor on biopsy. The patient was then referred to our hospital for surgery. Laparoscopic ascending colectomy was performed to treat the ascending colon cancer. Histopathological and immunochemical studies confirmed that the tumor of the ascending colon was a metastasis from the breast cancer. Although gastrointestinal metastasis from breast cancer is rare, and colon metastasis is even rarer, it might be necessary to rule out the possibility of a metastatic colon tumor from breast cancer when treating patients with a colon tumor who have undergone surgery for breast cancer. Colon metastasis of breast cancer can be managed through surgical resection and medical treatment to improve the patient's quality of life and life expectancy.