Abstract: Objective To find out the molecular basis and genetic rule of ABO subtypeby genotyping and pedigree analysis of a sample suspected to be cisAB by serological examination. Methods ABO blood group was identified by blood group serology in all samples. Exons 6 and 7 of ABO gene were amplified by polymerase chain reaction (PCR) and sequenced. Results The results showed that thegenotype of the sample was ABO*cisAB.01/O.01.02. In the family investigation, it was found thatserological results of the other fourmembers were found to be inconsistent with positive and negative reactions, but the blood type characteristics were different. The sequencing results showed that all of them carried the ABO*cisAB.01 gene. Conclusion ABO* cisAB.01 gene can lead to weak expression of A/B antigen and stable inheritance. ABO blood groups can be identified by molecular biological methods in the detection of serological specimens with different positive and negative blood types. The samples with incompatible serological typing can be detected by molecular biology method to assist in the identification of ABO blood group.

Key words: cisAB blood group, ABO*cisAB.01, allele Pedigree analysis