To investigate the serological and molecular characteristics of a pedigree carrying an allele for ABO*BW.11 blood subgroup.The ABO blood type of 9 pedigree members were determined by serological methods. Exons 6 and 7 of the ABO gene were amplified by PCR and directly sequenced. The patient and her father were also subjected to clone sequencing analysis.Serological tests demonstrated that the proband and her younger brother had an ABw subtype, whilst her father and two daughters had Bw subtype. Clone sequencing found that the exon 7 of the ABO gene of the proband had a T>C substitution at position 695, which was identified as a BW.11 allele compared with the reference sequence B.01. This BW.11 allele was also identified in the proband's father, brother and two daughters. Due to allelic competition, the A/BW.11 and BW.11/O alleles demonstrated significantly different phenotypes.The c.695T>C substitution of the ABO gene may lead to allelic competition in the Bw11 subtype. Combined molecular and serological methods is helpful for precise blood grouping.