In order to elucidate the expression and molecular genetic background of ABO gene seven samples with ABO discrepancy further identified as bi-specific ABO gene were studied. All these samples were subjected to phenotyping by monoclonal and polyclonal antisera and were then genotyped by direct DNA sequencing and haplotype-sequencing at the exon 6 and 7 of ABO gene. As a result, six ABO dual-specific alleles were identified in Chinese population. An antigen expressed by these B (A) or Cis-AB individuals varied from very low level to the normal level, compared with common A blood group samples. In conclusion, molecular genetic backgrounds of two pairs out of four samples in all samples were the same, however, the ABO expression showed diverse.