To analyze the molecular genetic basis for a case of ABw07 phenotype of ABO subtype.The ABO group antigens on red blood cells of the proband were identified by monoclonal antibodies and the ABO antibody in serum was detected by the standard A, B and O cells. The exons 6 and 7 of the ABO gene was amplified by PCR and the PCR product was sequenced directly after enzyme digestion. The amplified product was also cloned by TOPO TA cloning sequencing kit to split the two alleles apart, chosen colonies were sequenced bidirectionally. The samples of the parents and one sister of the proband were collected, then the blood group serological test and sequence analysis for exon 6 to 7 of ABO gene were performed.Both A and B antigen were detected on red blood cells of the proband and there was anti-B antibody in the serum. There was no 261G deletion. And the 297A/G, 467C/T, 526C/G, 657C/T, 703G/A, 796C/A, 803G/C, 930G/A, 1055G/A and 1096A/G loci were heterozygotes by direct DNA sequencing, which can be assigned for A102Bw07 genotype. After cloning and sequencing, two alleles of A102 and Bw07 were obtained. The Bw07 has one nucleotide change of G to A at nucleotide 1055 compared with B101, which results in an amino acid change from Arg to Gln at nucleotide 352. The Bw07 in the proband was inherited from his mother, and the serological characteristic of the ABO blood group and the sequence of exons 6 and 7 of the mother were the same as that of the proband.The G to A at nucleotide 1055 of alpha -1, 3 galactosyltransferase gene (B gene) can result in BW7 phenotype, with anti-B antibody in serum.