Factor B(BF), C2 and C4 are located in the Class III region of the major histocompatability complex in the short arm of chromosome 6. Two common alleles, Bf^*S, Bf^*F and Bf^*F1, Bf^*S07, Bf^*Fb1 have been reported. The genetic polymorphism study of BF was carried out by IEF and immunoblotting using anti-human properdin factor B serum. The level of Factor B was measured by SRID. The EDTA plasma samples were collected from 298 unrelated healthy Korean and 11 Korean family with three offsprings. The distributions of the Bf S, Bf FS, Bf F, Bf Fb1S, Bf Fb1, Bf SSO7, Bf FS07 are 71.5%, 18.8%, 6.4%, 2.0%, 0.3%, 0.7%, 0.3%, respectively. The Bf^*Fb1 allele was observed to be autosomal codominant with mendelian inheritance by family study. Bf allele frequencies differ in the various ethinic groups. The Bf Fb1 gene is very rare in Caucasian and Negroid although Bf Fb1 gene occurs in high frequency in Mongoloid; Korean (0.013), Japanese (0.015), Chinese (0.010). Bf Fb1 allele seems to be strongly related with C4^*A3 and C4^*B2. The mean protein level of Bf FbIS is 29.39±5.79 ㎎/dl and that of Factor B varies in the order of Bf FbIS> Bf F> Bf FS> Bf S. The family study indicates that the Bf Fb1 allele is an autosomal codominant gene and characteristic gene of Oriental. The protein level of Bf Fb1S is higher than that of Bf FS. Therefore, Bf^* Fb1 is a useful genetic marker for anthropologic study.