A 3-year-old nulliparous female Siamese suspected of pyometra with vomiting and abdominal dilatation and depression, was revealed to have atresia vaginalis with hypoplasia of vestibulo-vaginal junction after ovariohysterectomy. The both uterine horns and vagina were dilated containing large amount of bloody contents. The vagina was separated from the vestibulum by some connective tissue. The uteus and vagina were histologically almost normal except for severe hemorrhage in the uterine mucosa.