Abstract: Objective　To investigate the factors of inducing the unconformity of forward and reverse ABO blood typing caused by irregular antibody.  Methods　　The results of serological tests of blood typing in 12 cases were analyzed, and the factors of irregular antibody inducing the unconformity of forward and reverse ABO blood typing were tested for irregular antibody screening and identification and corresponding blood typing determination. Reverse ABO blood typing were repeated with red blood cells which corresponding antigens were negative.  Results　The amounts of alloantibodies among 12 patients were 4 anti-M，1 anti-N，1 anti-M combined anti-N，1 anti- Le^a，1 anti- P₁，1 anti-I，1 anti-D，1 anti-E and 1 anti-A₁. The result of repeated reverse blood typing with corresponding antigens being negative blood cells matched forward blood typing.  Conclusions　Samples with unconformity of forward and reverse ABO blood typing caused by irregular antibody can be identified correctly.

Key words: Blood typing, Irregular antibody, Antibody screening, Antibody identification