To investigate the molecular characteristics of Bw subgroup of ABO variant.Two individuals with Bw phenotypes were confirmed by standard serological assays. ABO genotype was analyzed with polymerase chain reaction-sequence specific primer (PCR-SSP) method. Exons 6-7 of B genes were amplified by specific PCR, and the PCR product was subjected to direct sequencing.The probands were identified as Bw phenotype by serological assays. As detected by PCR-SSP, the genotypes of the two probands were both B/O2. Compared with the wild-type B101, the B allele in one individual has harbored a missense mutation (C721T) in exon 7, which resulted in an amino acid substitutions (R241S). In the second individual, the B allele has harbored a missense mutation (C278T) in exon 6, which also resulted in an amino acid substitution (P93L).A Bw03 allele and a Bw12 allele were identified, which resulted in varied intensity of B antigen expression.