The measurement of anti-blood group A/B (anti-A/B) IgG antibody levels is important for ABO unmatched-organ recipients because the effective removal of the antibodies improves their prognosis. Living-donor liver transplantation (LDLT) into ABO-unmatched patients tends to have a very poor outcome due to major complications such as intrahepatic bile duct complications and hepatic necrosis. Sustained bile duct complications are associated with high preoperative IgM type anti-A/B Ab titers, while patients with high preoperative IgG type anti-A/B Ab titers frequently develop sustained hepatic necrosis. There are several existing methods by which anti-A/B Ab levels can be measured, including the standard tube (TT) method, an enzyme-linked immunosorbent assay, and a flow cytometry method. Anti-A/B IgG Ab is difficult to identify by the TT method, which is the most popular method and is based on the detection of hemagglutination, because the major isotype that facilitates red cell agglutination is the pentameric IgM molecule. Therefore, we have developed a method based on surface plasmon resonance (SPR) that detects the presence of the antigen-antibody complex without any labeling. This method allows us to rapidly quantitate anti-A/B IgG Ab levels.