Angiosarcoma is a malignant vascular neoplasm that usually involves the skin or soft tissues. A primary rectal angiosarcoma is exceedingly rare. A 77-year-old female was admitted to the hospital for evaluation of constipation and hematochezia. The patient had a history of uterine cervix carcinoma which was treated with surgery and radiation therapy. A colonoscopy revealed a friable, ulceroinfiltrative tumor with multiple hyperemic mucosae in the rectum. Microscopically, the tumor exhibited vasoformative growth with nuclear atypism and numerous mitoses. The tumor cells were strongly positive for CD31, CD34, and Factor VIII. We report a case of rectal angiosarcoma that developed after radiation therapy.