A 29-year-old man wanted to receive an ABO-incompatible kidney transplant. His blood type was O, and the donor, his father, was A1. After endoscopic splenectomy performed before kidney transplantation, the recipient developed a high fever and leukocytosis, and he was treated with antibiotics and 5 g of human immunoglobulin products by intravenous infusion for 3 d. Soon after the infusions, his anti-blood type A antibody titer (anti-A titer) rose, and several sessions of plasma-exchange (PEX) and double-filtration plasmapheresis (DFPP) failed to lower it. Three courses of anti-CD20 monoclonal antibody were administered to suppress the antibody production more specifically, and the rituximab infusions and repeated PEX and DFPP session lowered the anti-A titer and enabled kidney transplantation. Mild humoral rejection was observed 16 d after transplantation, but the recipient's serum creatinine was 1.5 mg/dL when discharged from the hospital. The increased anti-A titer may have been due to immunization by blood-type A antigen, with the human immunoglobulin products given to the patient being the source of the antigen. Administration of human immunoglobulin products to recipients of ABO-incompatible kidney transplants should be avoided, because it may cause an unexpected increase in anti-blood-type antibody titer.