A 9-month-old female Shar Pei cross-bred dog was presented with a history of recurrent rectal prolapse over 7 months. Repeated reduction and anal purse string sutures and subsequent incisional colopexy failed to prevent recurrent rectal prolapse. Digital rectal examination following reduction of the prolapse identified a faeces-filled sac within the ventral wall of the rectum and an orifice in the ventral colonic wall, cranial to the pubic brim. A ventral, communicating tubular colonic duplication was diagnosed by means of a barium enema. Surgical excision of the duplicated colonic tube was performed via a caudal ventral midline laparotomy. At 20 weeks post-operation, there has been no recurrence of rectal prolapse.