Data of the prevalence of red cell alloantibodies in blood donors will assist in improving safe blood supply for patients needing transfusion. The purpose of this study was to determine prevalence of red cell alloantibodies in Lao blood donors. Antibody screening and identification by multiple phase indirect antiglobulin standard tube assay were performed in serum samples from 1,181 blood donor individuals following routine work at the Lao Red Cross National Blood Transfusion Center. The overall prevalence of alloantibodies was 3.90%. All of the antibodies found were naturally occurring antibodies. Anti-P1 was the most common with a frequency of 1.95% followed by anti-Le(a), anti-Le(b), anti-Le(a+b), anti-M, anti-P1 plus anti-Le(a), anti-P1 plus anti-Le(a+b) with the prevalence of 0.59%, 0.42%, 0.42%, 0.17%, and 0.08%, respectively. This is the first report about prevalence of red cell alloantibodies among Lao blood donors. The information obtained from this study will be useful for safe blood transfusion and preparation of in house antisera.