Background: Atorvastatin metabolized by cytochrome P450 3A4 reportedly reduce the metabolism of clopidogrel into active metabolite, thus attenuating its inhibition of platelet aggregation ex vivo. We compared the effect of atorvastatin 10 mg versus 40 mg in clopidogrel resistance and clinical events after coronary stenting in patients with acute coronary syndrome. Methods: Platelet aggregation was measured before clopidogrel administration, 4 hours, 24 hours, and 5 days after the clopidogrel administration in 130 consecutive patients with acute coronary syndrome. Stented patients were randomly assigned to either atorvastatin 10 mg (n=65) or 40 mg (n=65), and received an oral loading dose of 300 mg of clopidogrel followed by 75 mg/d for 8 months. Measurement of platelet aggregation was done by the turbimetric method with the addition of adenosine diphosphate 5 關mol/L with continuous stirring at 1300 rpm. All patients received aspirin. Clinical events such as death, myocardial infarction, and target lesion revascularization were compared during the follow-up. Results: Percent platelet aggregation was 32.7 짹 20.4, 24.9 짹 14.1, 31.3 짹 16.9 (4 hours, 24 hours, and 5 days after 300 mg of clopidogrel pretreatment, respectively) in the Atorvastatin 10 mg Group. Percent platelet aggregation in the Atorvastatin 40 mg Group was 33.6 짹 13.9, 27.4 짹 14.9, 26.8 짹 17.8 (4 hours, 24 hours, and 5 days after 300 mg of clopidogrel pretreatment, respectively). No significant differences in percent platelet aggregation were noted between the 2 groups. Two cases of subacute stent thrombosis were found only in the Atorvastatin 40 mg Group. Clinical events such as death (no death in both groups), myocardial infarction (0 patient in the Atorvastatin 10mg Group vs. 1 patients in the Atorvastatin 40mg Group, p=0.857), and TLR (3 patient in the Atorvastatin 10mg Group vs. 2 patients in the Atorvastatin 40mg Group, p=0.737), demonstrated no significant differences during the follow-up. Conclusion: Atorvastatin 10 mg and 40 mg coadministered with clopidogrel for 8 months does not effect the antiplatelet potency of clopidogrel and showed no significant difference in clinical events in patients with acute coronary syndrome.