A 53-year-old woman visited the hospital of this study complaining of constipation. Colonoscopy revealed a circumferential tumor with severe stenosis, and a computed tomography scan showed neoplastic lesions in the rectum and right breast area. Histology was poorly differentiated adenocarcinoma, requiring differentiation between type 4 and metastatic rectal cancer. Additional immunohistochemical tests were performed and a rectal metastasis of breast cancer diagnosis was made. Hormonal therapy was effective and the tumor volume was significantly reduced. Rectal metastasis of breast cancer is said to be rare. However, in the case of patients diagnosed with breast cancer or with a history of breast cancer, considering the possibility of gastrointestinal metastasis using histopathological examination is important.