Pure red cell aplasia (PRCA) is a complication of ABO-incompatible allogeneic stem cell transplantation. The mechanism is not well known, although the isoagglutinin titer before transplantation or cyclosporine use is considered to be the cause. Patients with this complication require more blood transfusions than those without it. There is no standard treatment. We report two cases of PRCA after allogeneic peripheral blood stem cell transplantation that were successfully treated with plasma exchange and low-dose steroid.