Genetic polymorphism of esterase(Es) in 132 Korean race horses was studied by starch gel electrophoresis. Three different Es phenotypes were identified as Es FI, Es II and Es IS. Their respective frequencies were 13.64%, 78.03% and 8.33%. The distribution of the observed Es phenotypes agreed with Hardy-Weinberg expectations. Therefore, it is assumed that Es phenotypes in Korean race horses are genetically controlled by three codominant alleles, ES^F, ES^I and Es^S at a single locus. The allele frequencies of Es were Es^F 0.068, Es^I 0.890 and Es^S 0.042.