Background: To achieve more effective and safe antiplatelet therapy in the periprocedural phase, we think that an additional loading dose of 200 mg of cilostazol combined with aspirin and clopidogrel may be efficacious, reducing acute stent thrombosis and complication rates. Therefore, we sought to investigate the loading effects on platelet inhibition in patients undergoing percutaneous coronary intervention (PCI). Methods and results: From December 2008 to July 2009, 100 consecutive patients, who underwent PCI with drug-eluting stents (DES) insertion, were enrolled and assigned to receive dual antiplatelet therapy (loading dose: 300 mg of aspirin and 300 mg of clopidogrel, n = 50) or an additional loading dose of 200 mg of cilostazol (n = 50). All loading doses of antiplatelet agents were administrated at least 3 hours before PCI procedure and platelet function test were performed just before and 24 hours after the procedure using light transmission aggregometry (Chrono-Log, Havertown, PA, USA), VerifyNow짰 system assay (Accumetrics, San Diego, CA, USA). Comparing baseline and angiographic characteristics between two groups, there were no significant differences. Laboratory results revealed that an additional loading dose of 200 mg of cilostazol showed more effective than dual antiplatelet therapy, improving responsiveness and reducing drug resistance to aspirin and clopidogrel(table). Conclusion: Initial loading therapy of cilostazol before the procedure could improve platelet responsiveness and reduce resistance to antiplatelet drug in patients undergoing PCI with DES.