Human orosomucoid (ORM) is a major binding protein for various basic drugs. The genetic polymorphisms of ORM could be responsible for interindividual variation in the plasma binding of basic drugs, which might influence their effects or toxicities. The genetic polymorphisms of ORM on the Han population in Nanjing of China were analyzed by isoelectric focusing (IEF) on polyacrylamide gels following by immunoblotting. After desialylation of sera from 220 unrelated Chinese subjects, the band patterns of ORM showed that the polymorphism of the structural locus ORM1 is controlled by three codominant autosomal alleles, ORM1*F1, ORM1*F2 and ORM1*S, which presented five phenotypes, ORM1 F1, ORM1 S, ORM1 F1F2, ORM1 F1S, and ORM1 F2S. The allele frequencies were: ORM1*F1=0.7068, ORM1*F2=0.0182, ORM1*S=0.2750. The results presented in this paper indicate the ORM1 locus is polymorphic and the ORM2 locus is monomorphic in sera from the Han population in Nanjing of China.