A 3-month-old intact male, Labrador retriever was presented with the history of coagulopathy and anemia. The results of initial screening tests of the hemostatic system yielded a tentative diagnosis of hemophilia. Activated partial thromboplastin time (APTT) was distinctly prolonged (106 seconds) and prothrombin time (PT) was not detected due to markedly prolonged test time. Whole blood transfusions (20 me l/kg body weight) were carried out prior to assays of coagulation factor. After transfusion, the patient recovered well and hemorrhage ceased. Blood samples were assessed for coagulation factor activity. The patient showed markedly low factor IX coagulation activity (5%, reference range: 7~140%) and was diagnosed with hemophilia B. After recovery, the patient was discharged from the hospital. However, 4 months later the patient was re-hospitalized for recurrence of the initial symptoms. The owner did not want to pursue further treatment and the patient died of respiratory distress two days later.