Background : Statin is frequently co-administered with clopidogrel in patients who underwent PCI. Drug interaction between clopidogrel and lipophilic statin is an important but still controversial issue in the DES era. In CILON-T trial, prospective RCT, we compared the platelet inhibitory effect of clopidogrel according to statin types (lipophilic atorvastatin vs. hydrophilic rosuvastatin). Method and Results : A total of 280 patients (mean age 62.5 years, 63.1% men) planned to implant DES were prospectively randomized by 2x2 factorial design to four groups according to statin types (rosuvastatin 10mg qd vs. atorvastatin 20mg qd) and the use of cilostazol (control vs. cilostazol 100mg bid ) from Sep 2006 to July 2007. After successful PCI, platelet function test using VerifyNow P2Y12짰 was performed at discharge and after six months (n=90). We analyzed absolute P2Y12 receptor reaction unit (PRU) and the percentage of P2Y12 receptor inhibition compared to baseline (P2Y12 inhibition %) at six months. There were no differences among four groups in clinical characteristics including age, sex, hypertension, DM and hyperlipidemia. Patients administered with atorvastatin achieved less platelet inhibition than patients with rosuvastatin, even if they were backed up with cilostazol. One case of cardiac death and one case of stent thrombosis occurred and they were all in atorvastatin / control group. Conclusion : Atorvastatin showed more drug interaction with clopidogrel compared to rosuvastatin. This drug interaction disturbing clopidogrel���s efficacy was not compensated by the use of additional antiplatelet agent, cilostazol.