A broodmare showed mild signs of abdominal discomfort and anemia after normal delivery. Ultrasonographic examination revealed a massive hematoma within the broad ligament adjacent to the uterine horn. Internal bleeding into the peritoneal cavity (hemoabdomen) was not seen. Following treatment, the clinical signs improved. Hemorrhage caused by rupture of the arteries within the broad ligament of the uterus may be a cause of hematoma. Prepartum and postpartum rupture of the arteries supplying the reproductive organs in the mare, which is not uncommon, can be fatal if severe hemoabdomen occurs. In the present case, the hematoma was considered to be tightly encapsulated between two serosal membrane layers of the broad ligament, and the membranes had remained intact. Thus, the serosal membranes did not split open, and massive bleeding into the peritoneal cavity did not occur. For this reason, the present broodmare avoided potentially fatal hemorrhagic shock.