Mimicking antibody is a specific antibody that is adsorbed on both antigen-positive and -negative erythrocytes.Mimicking antibodies can be classified into two categories: alloantibody-like mimicking antibodies and autoantibodylike mimicking antibodies. Since alloantibody-like mimicking antibodies induce the same reaction as alloantibodies, it is necessary to accurately understand the history of blood transfusion and pregnancy. Meanwhile, autoantibody-like mimicking antibodies show specificity for antigens possessed by the patient, facilitating identification. However, blood selection in RBC transfusion is hampered by the risk of alloantibody production, and the clinical significance of autoantibody-like mimicking antibodies must be considered.Here, we report the case of a patient with an alloantibody-like mimicking anti-c identified after long-term transfusion of R1R1 RBC due to possession of anti-E, and of a second patient with an autoantibody-like mimicking anti-E by first testing in the absence of a history of transfusion and pregnancy.