The genetic polymorphisms for the esterase-7 (Es-7), esterase-8 (Es-8), esterase-10 (Es-10) and Transferrin (Tf) were studied in testis, heart and plasma tissues of Korean (Seoul rat (Rattus norvegicus) population using polyacrylamide gel electrophoresis, isoelectric focusing and immunoblotting. Two phenotypes of Es-7 in testis, Es-7AB (13.79%), Es-7B (86.21%) were found. The allele frequencies of Es-7^*a and Es-7^*b were 0.069, 0.931, respectively. Four phenotypes of Es-8 in heart, Es-8A (1.39%), Es-8AB (12.50%), Es-8B (81.94%) and Es-8BC (4.17%) were found. The allele frequencies of Es-8^*a, Es-8*b and Es-8^*c were 0.076, 0.903, 0.021, respectively. Four phenotypes of Es-10 in heart were Es-l0A (81.94%), Es-10AB (12.50%), Es-10B (1.39%) and Es-10AC (4.17%). The allele frequencies for the Es-10^*a, Es-10^*b and Es-10^*c were 0.903, 0.076, 0.021, respectively. Finally, Tf phenotypes in plasma was identified to be Tf1-1 (96.81%) and Tf2-1 (3.19%). The allele frequencies of Tf^*1 and Tf^*2 were 0.984, 0.016, respectively.