We report herein the rare case of a 56-year-old woman who suffered vaginal rupture into the peritoneal cavity during sexual intercourse, through which the small intestine prolapsed out from the vaginal opening. The patient had undergone abdominal hysterectomy 4 years earlier. An emergency laparotomy was performed which revealed rupture in the posterior fornix of the vagina and peritonium through which prolapse of the small intestine had occurred. The prolapsed intestine was pulled back into the pelvic cavity, and the vagina and peritonium were repaired. Macroscopically, the operative findings revealed no inflammatory changes or evidence of malignancy in the abdominal cavity. Thus, although rare, a ruptured vagina caused by sexual intercourse should also be considered in the field of surgery, even when a middle-aged woman presents with acute abdominal symptoms without a history of any other traumatic episode.