Background: It has been demonstrated that clopidogrel (Plavix짰) doses of 525-600mg are needed to produce a potent inhibition of platelet aggregation induced by adenosine diphosphate (ADP) within 2 hours. However, it is unclear that whether the platelet inhibition provided by high loading dose before percutaneous coronary intervention (PCI) with drug-eluting stent (DES) is clinically safe and effective in terms of clinical outcomes, bleeding and vascular complications, especially for the Asian population whose body weight is less than western countries. Methods: A total 296 patients (pts, Male 156, mean age, 62.3 짹 9.5 years) were randomly assigned to receive 300, 450 and 600 mg of clopidogrel before undergoing PCI. Aspirin 100mg and 50 U/kg of unfractionated heparin were administered as the routine antiplatelet and antithrombotic regimen. Medium to high loading dose (450 and 600 mg, n=152) group (Group 1) was compared with Standard dose (300mg, n=144) group (Group 2) in terms of in-hospital complications, bleeding and vascular access complications. Results: Baseline characteristics including body weight (Group 1, 66.7 kg, Group 2, 64.5 kg, p=NS) were similar in both groups. Although mean ACT level was higher in Group 1 (276.3짹51.8 vs. 224.3짹82.1 in Group 2, P=0.03), the incidence of major bleeding was not different between the two groups (3.7% vs. 11.1% in Group 2, P=0.83). Vascular access complications including AV fistula, pseudoaneurysm were also similar between the two groups. Although it was not statistically significant, Group 1 showed numerically lower rate of ischemic chest pain (5.9% vs. 25.5%, P=0.89) and ischemic EKG changes (2.0% vs. 15.7%, P=0.45). Early clinical outcomes such as death, myocardial infarction, target lesion and vessel revascularization and major adverse cardiac events were similar between the two groups up to 1 month follow up. Conclusion: Medium to high loading dose (450 mg and 600 mg) clopidogrel administration in pts undergoing contemporary PCI using DES in Asian population seems to be clinically safe and feasible compared with the standard dose clopidogrel (300mg) without increasing overall bleeding and vascular complications.