Backgrounds : It has been suggested that inter-individual variation of anticoagulation effect is associated with the polymorphism of certain genes including VKORC1. VKORC1 has a common promoter variant (c.-1639G>A) that reduces the expression of the gene, and therefore alters sensitivity of warfarin. Objects : The purpose of this study is to determine the frequency of VKORC1 variants in Korean patients population and to evaluate the association between VKORC1 polymorphism and warfarin dose requirement. Methods : Total 68 patients from outpatient clinic of Cardiology at Kyungpook National University Hospital were genotyped for SNP(Single Nucleotide Polymorphism) in the VKORC1 gene. Results : Eleven of 68 subjects (16.2%) were heterozygous and fifty-five (80.9%) were homozygous for VKORC1 polymorphism(-1639G>A). Mutant allele frequency of VKORC1 was 89% in Korean subjects, similar to that of Asian population reported in other studies. There was no difference in maintenance dose of warfarin between the two groups, mutant and wild types of VKORC1(p=1.00). Also, both warfarin dose and prothrombin time(PT) stability presented by coefficient of variation (CV) showed no association with VKORC1 polymorphism(p=0.956 and 0.616, respectively). Conclusion : It is known that the polymorphism of VKORC1 gene is responsible for warfarin sensitivity and patients who are carriers for polymorphism require lower maintenance dose of warfarin. However, in this study, there was no association between VKORC1 polymorphism and warfarin dose requirements in small group patients.