To explore the molecular basis of an individual with A subtype of the ABO blood group.The ABO antigen and serum antibody of the proband and his parents and sister were detected by a serological method. The whole coding regions of the ABO gene were amplified by PCR and subjected to bidirectional sequencing.Red blood cells of the proband showed mixed field agglutination with anti-A but did not agglutinate with anti-B, and his serum did not agglutinate with A and O cells but with B cells. The proband was identified as an Aw phenotype. Heterozygous status of 1A/G, 106G/T, 188A/G, 189C/T, 220C/T, 261G/del, 297A/G, 467C/T, 646A/T, and 681A/G of the coding region of the ABO gene were identified by directly sequencing of the proband. The serological characteristics and nucleotide sequences of the mother were similar to those of the proband. However, the ABO genotypes of his father and sister were B101/O02 and O02/O02. The proband therefore has carried an O02 allele and a novel allele. Compared with A102, the novel allele contains 1A>G, which resulted in translation-initiator code change and was nominated as Aw43 by dbRBC of NCBI.An Aw43 subtype has been identified for the first time, which may be attributed to the 1A>G and 467C>T variants on the α1,3-N-acetyl-galactosaminyltransferase gene.