To identify the genotypes of the blood sample whose blood grouping showed discrepancies and study the ABO alleles' molecular characteristics of the involved ancestry. Blood samples were preliminary genotyped by PCR-SSP. Complete exon 6 and 7 in the ABO genes were amplified by PCR and the PCR products were directly sequenced and cloning sequenced to identify its genotype. Sequence analysis indicated that 3 samples of the family had an nt905A>G mutation in the B gene compared with ABO*B101. Combined with the serological results, the propositus could be typed as Bx02/O102. DNA sequencing analysis is able to identify the serological phenotype samples that forward and reverse group methods were incongruous.