Background and Objectives: It is important to achieve an appropriate balance between potent efficacy of platelet inhibition and increased bleeding of antiplatelet therapy. The aim of this study was to investigate benefits of loading dose of 200 mg cilostazol in addition to aspirin and clopidogrel of 300 mg on inhibition of platelet aggregation compared to loading dose of 300 or 600 mg clopidogrel in addition to aspirin of 300 mg. Subjects and Methods: Forty-five patients were enrolled and randomly received three different regimens of loading dose as ratio of 1:1:1. All regimens were given within 6 to 12 hours prior to percutaneous coronary intervention (PCI). High residual platelet reactivity (HPR) was measured assessed by light transmittance aggregometry with 10-µM adenosine diphosphate and VerifyNow assay just before PCI. Results: Low loading dose group of 300-mg clopidogrel revealed higher rate of HPR compared to both 200-mg cilostazol and 600-mg clopidogrel groups (p <0.05). In comparison of 200 mg cilostazol to 600 mg clopidogrel, there was no significant difference of HPR. Conclusion: Adjunctive loading dose of 200 mg of cilostazol can achieve appropriate degree of platelet inhibition compared to high loading dose of 600 mg clopidogrel. Key words: Cilostazol, Platelet function tests, Drug-eluting stents