Hematometra is defined as the accumulation of blood and blood clots in the uterus. An 8-month-old, intact female Poongsan dog presented with continuous severe hemorrhagic vulvar discharge and anemia. The initial diagnostic evaluation included abdominal ultrasonography, radiography, and physical and laboratory examinations. The electrolyte levels were low: Na ion levels were 128 mmol/L (reference range, 141 - 152 mmol/L), and Cl ion levels were 99 mmol/ L (reference range, 105 - 115 mmol/L). At presentation, the white blood cell count was 60.19 × 103/μL (reference range, 5.05 – 16.76 × 103/μL), packed cell volume was 11.8% (reference range, 37.3% - 61.7%), hemoglobin levels were 4.6 g/ dl (reference range, 13.1 - 20.5 g/dl), and platelet count was 48 × 103/μL (reference range, 148 - 484 × 103/μL). Based on the results of the complete blood count, the dog was given lactated Ringer’s solution and a whole blood transfusion. On abdominal ultrasonography, the left uterine horn was enlarged and filled with echogenic fluid. On laparotomy, the uterus was enlarged and showed an accumulation of blood and blood clots. The incised uterine horn revealed that the endometrium was filled with blood and blood clots and had a cystic appearance. Additionally, thick and yellowish pus had accumulated in the uterine cavity. Gross findings revealed a definitive diagnosis of cystic endometrial hyperplasia- pyometra complex with severe hemorrhage, termed hematometra. This case was the first report of severe hematometra in a young Poongsan dog.