Background and Objective: Recent evidences suggested that aspirin or clopidogrel resistance is associated with poor cardiovascular outcomes such as recurrent atherothrombotic events and stent thrombosis (ST) after drug eluting stent (DES) implantations. Therefore, we sought to prospectively evaluate the incidence of stent thrombosis by definitions of the Academic Research Consortium (ARC) and their responsiveness to aspirin and clopidogrel in patients with ST and non-ST. Method: We enrolled consecutive 409 patients (274 males, 63.5짹10.6 years) who received DES implantations. ST was defined by ARC definition. Aspirin and clopidogrel responsiveness were evaluated by VerifyNow��� tests (Accumetrics Inc, CA). Aspirin resistance was defined as an aspirin reaction units (ARU) ��� 550. Clopidogrel resistance was defined as the less than 20%.inhibition of P2Y12 receptor. Results: Baseline demographic characteristics were similar between ST and non-ST group. ST occurred in 12 patients (2.9 %) who were 8 of definite, 3 of probable and 1 of possible. 9 patientsts of the ST had clopidogrel resistance and 3 of the non-ST. (p=0.015) All patients of the ST hadnot aspirin resistance. The ARU values were not different between the ST and non-ST group (430.6 짹 40.8 vs. 436.7 짹 66.9, p=0.624). In the ST, the % inhibition of P2Y12 receptor was lower than non-ST group (18.8짹13.9 vs. 29.9짹23.2, % p=0.026). Conclusions: The lower responsiveness of clopidogrel but not aspirin is associated with stent thrombosis after drug eluting stent implantations in consecutive patients with DES implantation.