To evaluate polymorphisms and gene frequencies in Korean (Seoul) house rat (Rattus norvegicus) population, esterase-2 (Es-2), transferrin (Tf) and albumin (Alb) were investigated by starch gel and isoelectric focusing electrophoresis. Among 51 individuals investigated, Es-2 phenotypes were Es-2C (49.02%), Es-2CD (25.50%), Es-2D (19.6%), Es-2A(1.96%) and Es-2AC (3.92%). The gene frequencies of Es-2^c, Es-2^d, and Es-2^a were 0.673, 0.323 and 0.039, respectively. Among 51 individuals investigated, Tf phenotypes were Common type (49 individuals) and two variant types (2 individuals). Alb phenotype was monomorphic in 51 individuals of wild rat. But, the investigators found the difference of electrophoretic band pattern between wild and laboratory rats.