Background: Clopidogrel resistance could be associated with recurrent therothrombotic events after drug eluting stent (DES) implantations. This study examines whether patient resistance to clopidogrel is associated with thrombotic event period after drug eluting stent (DES) implantation. Methods: We reviewed 1344 patients with DES implantation from Jan. 2005 to Jan. 2009. Clopidogrel resistance was defined as the less than 20% inhibition of P2Y12 receptor assessed by VerifyNow��� tests (Accumetrics Inc, CA). All patients were reviewed occurrence of composite thrombotic events, including stent thrombosis, cardiovascular death, non-fatal myocardial infarction. Results: Clopidogrel resistance was presents in 506 patients (37.9%). Composite thrombotic events occurred in 4.2% of clopidogrel resistance group, however in 2.2% in non-resistance group (p=0.034). The stent thrombosis occurred in 20 patients (4.0%) in resistance group, and 13 patients (1.6%) in non-resistance group (p=0.007). In the subgroup analysis, acute and subacute stent thrombosis occurred in 9 patients (45%), late and very late stent thrombosis was 11 patients (55%) in clopidogrel resistance group, whereas only late and very late stent thrombosis occurred (13 patients, 100%) in clopidogrel response group (p=0.003). The hazard ratio of clopidogrel resistance for composite thrombotic events was 2.18 (95% CI=1.028 to 4.614; p=0.042). Conclusion: Clopidogrel resistance is an independent risk factor of stent thrombosis in patients with DES implantation. Moreover, the stent thrombosis usually occurred in early period in the clopidogrel resistance group than the non-resistance group.