A seven-years-old, intact Terrier bitch was admitted to our clinic with the history of loss of appetite, enlargement of abdomen, constipation and anuria. Distended part of the abdomen thought to be the bladder and abdominocentesis was performed. A kind of thick, viscous fluid was taken by this procedure. Abdominal ultrasonography revealed enlargement of the uterine horns filled with a hypoechoic fluid ventro-cranially located from the bladder. It was firstly diagnosed as pyometra and ovariohysterectomy performed. At ovariohysterectomy, it was found only one dilated uterine horn stuck to the vesica urinaria and hypoplasia of the ipsilateral cornu uteri. The uterine fluid was found to be aseptic microbiologically and it was diagnosed as hypoplasia of the cornu uteri and mucometra.