The genetic variation of antithrombin III (ATIII) in Korean population was investigated by using the methods of isoelectric focusing and immunoblotting. One common allele (ATIII*1) and two rare alleles (ATIII*2 and ATIII*5) were observed. But, other rare alleles (At*3 and ATIII*4) were not. The frequencies for the alleles of ATIII were ATIII*1=0.9960, ATIII*2=0.0016 and ATIII*5=0.0024. The frequency of ATIII*1 in Korean population was higher than that and rare alleles were lower than those of German population.