OBJECTIVE To investigate the serological and molecular biological identification of B(A) blood group and its reasonable method of blood transfusion for patient with B(A) blood group. METHODS The blood group of patient was detected by serological method, at the some time, the genotype of patient was detected by using the ABO-TYPE Variant kit and sequence analysis of 6 and 7 exons in ABO gene; the washed O red blood cells were used to cross matching blood of difficultly matching blood by the three step analysis method. RESULTS The A weak and B strong agglutination were found in positive type, and A1C(3+), BC(-) were observed in negative type; the molecular biological identification showed B(A)04, 640 A > G; the matching blood main side of washed O red blood cells displayed no agglutination. CONCLUSIONS The identification and analysis of rare blood or subtype should be very careful; if necessary, the molecular biological detection should carried out; the blood transfusion for patient with rate blood group or subtype should be safe, correct and reasonable.