Background— The aim of this study is to evaluate the safety of the concomitant treatment with proton pump inhibitor (PPI) and clopidogrel in patients who underwent percutanous coronary intervention (PCI) and drug-eluting stent stent (DES) implantation. Methods and Results— We examined a history of PPI use at discharge from the hospital after PCI-DES implantation from January 2006 to January 2007 in our institute. We compared 76 patients (group I) who were prescribed PPI at discharege (at least for 14 days) and 440 patients (group II) who were not prescribed PPI. There were 44 peoples who have not visited our institute since PCI. We made a phone call to check the clinical situation of the patient. We considered the primary end point are stent thrombosis , death, myocardial infarction. We defined ST as a definite or probable according to ARC definition. A median clinical follow up duration was 1371 [1255-1476] days and a median duration of PPI use is 42 [20-65] days. Baseline clinical characterstics between two groups were not different, except higher prevalence of male sex in group II. Univariate analysis showed the incidence of primary end point between the both groups was not significantly different.[ 7.9% (n=6) for group I vs. 3.9% (n=17) for group II, p=0.130]. The incidence of ST between the both groups was not significantly different.[ 5.3% (n=4) for group I vs. 2.0% (n=9) for group II, p=0.109]. Cox regression analysis showed that PPI use is not related MACE. Conclusion- Our data suggest that a concomittant use of clopidogrel and PPI for short-term period does not significantly influence the clinical outcome in patients after PCI –DES implantation.