We here report a case of a 33-year-old woman who experienced secondary postpartum hemorrhage (PPH) due to uterine artery pseudoaneurysm rupture. She had intrauterine balloon tamponade for unexplained primary PPH after spontaneous vaginal delivery, and subsequent angiography showed no abnormal contrast extravasation. However, profuse vaginal bleeding occurred 22 days postpartum. Color Doppler ultrasonography demonstrated an anechoic mass with turbulent flow in the lower uterine segment, corresponding to uterine artery pseudoaneurysm. She was successfully treated with selective uterine arterial embolization. Decreased levels of von Willebrand factor and factor VIII led to the diagnosis of von Willebrand disease. When it is determined that a patient has unexplained PPH or uterine artery pseudoaneurysm, a high index of suspicion and further investigation for underlying bleeding disorders is warranted.