Backgrounds: The use of aspirin and clopidogrel reduced the incidence of ischemic complication in patient who underwent percutaneous coronary intervention (PCI), but significant rates of cardiovascular events persist. It might be related to variable effect of antiplatelet agents or some racial differences in platelets. So we investigated the relation between antiplatelet activity and in-stent restenosis in patients who underwent PCI. Methods: Ninety-three patients who underwent PCI and maintained 100mg of aspirin and 75mg of clopidogrel after loading dose (aspirin 200mg, clopidogrel 300mg) up to six months were enrolled for this study. They were taken routine 6-month follow up coronary angiography and platelet function test was performed by Chrono-log (model 490) Aggregometers. The aspirin resistance was defined by 5 關mol/l adenosine diphosphate (ADP)-induced aggregation ���70% or 0.5 mg/ml arachidonic acid-induced aggregation ��� 20%. Results: Thirteen patients (13.9%) was developed binary in-stent restenosis (ISR). But only two patients were resistant to aspirin and there was no binary ISR in these aspirin resistant patients. There was no stent thrombosis (ST) including acute, subacute and late thrombosis. Conclusions: Our result showed that the incidence of aspirin resistance were very rare in Asian. And there was no significant relation between aspirin resistance and ISR. It might suggest that in Asian people aspirin resistance is very rare compared to western people and it might not be contributed to restenosis of PCI.