The Ael subgroup expresses the least amount of A antigens and could only be detected by performing the adsorption-elution test. The frequency of the Ael subgroup is about 0.001% in Koreans, and the Ael02 allele, which originates from A102, is the most frequently identified allele in the Korean population. We report a Korean family with the Ael03 allele identified by molecular genetic analysis. To the best of our knowledge, this is the first such report in Korea to date.