Blood group antigens can be distributed differently within different nationalities. Therefore, information about the prevalence of blood group antigens in the Lao population will be useful for providing better blood transfusion services in the Lao People's Democratic Republic. The purpose of this study was to determine the prevalence of blood group antigens in Lao blood donors. Blood samples from 464 Lao national volunteer blood donors were typed for antigens in various blood group systems including ABO, MNS, P1PK, Rh, Kell, Lewis, Duffy, Kidd, and Diego. The results show similar antigen prevalence to that among Northeast Thais for ABO, MNS, P1PK, Rh, Kell, and Duffy systems. In the ABO system, 0 was the highest at 37.72 percent,followed by 35.56 percent B, 19.83 percent A1, 6.47 percent A1B,and 0.43 percent A2B. The common phenotypes were D+C+E-ce+at 60.43 percent, M+N-S-s+ at 46.55 percent, Fy(a+b-) at 80.82 percent, Jk(a+b+) at 39.44 percent, and kk at 99.72 percent.Interestingly, Le(a-b-) was found at 50.43 percent, which was significantly higher than previous reports in Thais and Taiwanese.The P1 antigen was found in only 18.97 percent, which is much lower than in Whites and Blacks. Rare phenotypes were Fy(a-b+)and Jk(a-b-), found at 0.22 percent and 4.31 percent, respectively.In terms of negative antigens the study shows 0.22 percent Fy(a-), 35.34 percent Jk(a-), 29.53 percent Jk(b-), 3.04 percent C-, 2.39 percent e-, and 5.17 percent M-. The high prevalence of C, e, and Fy" and immunogenicity of these antigens may induce alloimmunization in transfusion-dependent patients, creating difficulties providing blood from Lao donors. The information obtained from this study will be useful for improving transfusion therapy in the country, especially for estimation of the availability of compatible blood for patients who have produced antibodies.