Background: Asian populations was reported to have different prevalence of CYP2C19 polymorphisms compared with white populations. However, genetic differences between specific Asian ethnicities and their impact on clopidogrel response (phenotype) remain unclarified. Methods: We investigated the prevalence of CYP2C19 polymorphisms among 100 Korean, 100 Chinese, 100 Malay and 100 Asian Indian subjects. We then validated genotype-phenotype relationships using the vasodilator-stimulated phosphoprotein (VASP) assay in an independent cohort of 58 consecutive Asian patients on 75 mg clopidogrel daily. Results: Figure 1a shows the prevalence of homozygous CYP2C19*1 (non-carriers), heterozygous or homozygous *2 or *3 (loss of function, LOF carriers) while figure 1b shows their impact on clopidogrel responses between extensive metabolizer (EM), normal metabolizer (NM) and poor metabolizer (PM) by VASP assay. Heterozygous or homozygous *17 (gain of function, GOF carriers) genes are significantly higher prevalent in Indians (28%) than other three asian countries (< 5 %). Conclusion: In this population of 4 major Asian ethnicities, we observed a higher prevalence of LOF polymorphisms in Korean, Chinese and Malay subjects and a higher prevalence of GOF polymorphisms in Indian subjects. Compared to non-carriers, LOF and GOF polymorphisms significantly modified the pharmacodynamic response to clopidogrel. These data suggest the Indian population has totally different genetic background and phamacodynamic impact on clopidogrel therapy