Background; Low response to standard clopidogrel therapy (75mg/day ) assessed by a point-of-care assay has been associated with thrombotic events after drug-elution stent (DES) implantation. We hypothesized that high dose clopidogrel (150mg/day) or adding cilostazol (200mg/day) on standard clopidogrel could improve the clopidogrel resistance in patients with drug eluting stent implantations. Method: We selected consecutive 37 patients with clopidogrel resistance defined as a P2Y12 Reaction Unit (PRU) larger than 235 assessed by VeryfyNow P2Y12 assay (Accumetrics, San Diego, CA). We randomly allocated three groups; standard group (75mg/day of clopidogrel, 12 patients), high dose group (150mg/day of clopidogrel, 13 patients) and cilostazol group (adding 200mg/day of cilostazol, 12 patients). After 2 weeks of treatments, we reevaluated PRU value and % inhibition of P2Y12 receptor. Result; Baseline demographics were similar among three groups. Baseline PRU (group I, II and III) were 279.1짹46.5, 284.3짹43.8 and 286.3짹29.5, respectivly (p=0.902). PRU values after treatment were significantly lower in high dose and cilostazol group than standard group. (standard;283.5짹54.1, high dose; 226.3짹76.8 and cilostazol; 220.3짹63.1, p=0.001). % inhibition of P2Y12 receptor after treatment were significantlyhigher in high dose and cilostazol group than standard group. (standard; 13.9짹9.5, high dose; 20.9짹18.5 and cilostazol; 32.1짹22.%, p=0.001). Conclusion : Adding cilostazol and high dose clopidogrel could ameliorate low responsiveness of standard dose clopidogrel in patients with drug eluting stent implantation.