Genetic polymorphism of human Factor I in Korean population was studied using polyacrylamide gel isoelectric focusing electrophoresis (pH5-8) followed by immunoblotting technique. Among the 463 unrelated individuals, three phenotypes, FI A type (1.51%), FI AB (13.61%) and FI B (84.88%), were observed. Gene frequencies of FI^*A and FI^*B were estimated to be 0.0831 and 0.9169, respectively. In comparison with other population data, we may be assumed that the FI^*A allele frequency indicates a west-to-east geographical cline, ranging from France (0.0062) through Korea (0.0831) to Japan (0.1109). Therefore, these findings suggest that Factor I is very useful marker for population genetics and anthropogenetical studies.