We describe a case of retrograde intussusception due to a sigmoid colonic polyp. A 62-year-old man admitted with lower abdominal pain had a tumor palpated in the left lower abdomen. Ultrasonography showed a double intestinal structure. Barium enema disclosed a complete beak-like obstruction of the sigmoid colon. Following the diagnosis of mechanical obstruction, we conducted a laparotomy and found the sigmoid colon invaginated retrogradely into the oral side of the colon. The resected specimen revealed a pedunculated polyp in the mucosa, and microscopic examination clarified it to be tubulovillous adenoma. Although some cases of intussusception require ultrasonography and computed tomograpy, barium enema is useful in diagnosing retrograde intussusception.