Abstract: Objective: To analyze the main serological characteristics of B(A) subtype and the nature of red blood cell A antigen.Methods: Six cases of suspected B(A) subtype specimens detected in our laboratory were subjected to detailed serological and molecular biological tests.Results: Six specimens were confirmed to be B(A) subtype by molecular biology tests, 5 cases were B(A) 04 and one case was B(A) 02. The main serological characteristics of these 6 cases was that their red blood cells had obvious reactions with high titer monoclonal anti-A, but did not react with human-derived anti-A or monoclonal anti-A diluted to a titer of less than 256 at room temperature, in addition to the normal agglutination reaction with anti-B. The reverse-typing was consistent with that of normal bloodgroup B. These 6 cases of B(A) subtype red blood cells did not react with human-derived anti-A serum at room temperature, but were able to react after incubation at 4℃. Most cross-matching with donors of B blood group at room temperature or at 37℃ were compatible.Conclusion: Antigen A on B(A) human red blood cells may be a cold-reactive antigen, and its antigenic properties need further study.