The genetic variation of placental aconitase (ACON: E.C.4.2.1.3) was investigated in 311 Korean placentae by horizontal starch gel electrophoresis. We found that the numbers of individuals showing ACO1 1-1, ACO1 2-1 and 1 2-2 phenotype were 285(91.6%), 25(8.1%) and 1 (0.3%), respectively. The allele frequencies of ACO11 and ACO12 were 0.957 and 0.043. In contrast to the polymorphic phenotype of cytoplasmic aconitase (ACO1), mitochondrial aconitase (ACO2) was found to be monomorphic. Our results show that the allele frequencies in Korean population are similar to those of Japanese population. The results further confirm the previous suggestion that the frequency of ACO12 allele in Mongoloid group including Korean seems to be higher than that of other racial groups.