A 2-year-old female Maltese dog was presented with a history of anemia and vaginal hemorrhagic discharge. Physical examination revealed severe vaginal hemorrhagic discharge, abdominal pain, pale mucous membranes, low blood pressure and dehydration. Results of serum biochemistry, hematology, venous blood gas, and electrolyte canine C-reactive protein (CRP) test revealed severe normocytic normochromic anemia, severe neutropenia, a high level of CRP, hypoglycemia, and imbalanced electrolytes. Abdominal ultrasound examination showed focal hypoechoic defect with loss of layering in uterine horn wall. A laparotomy revealed a clear reddish fluid in the abdomen, the fistula of left and right uterine horn, the purulent discharge from fistula, and symptoms of septic peritonitis near by the fistula site. The bitch underwent ovariohysterectomy and recovered without complication. Histopathological diagnosis of the uterine fistula site was adenocarcinoma.