Background: Cilostazol (Pletaal짰) is a potent inhibitor of type III phosphodiesterase and has not only the antiplatelet therapy but also pleiotropic effect such as restoring or stabilization of endothelial dysfunction. We investigated the influence of cilostazol on acetylcholine (Ach)- induced drug-eluting stent (DES) associated coronary artery spasm (CAS) and 12 month clinical outcomes. Methods: Among 1862 consecutive patients (pts) treated with DES, 1010 pts underwent follow up coronary angiography (CAG). Among them, 160 pts underwent Ach provocation test by injecting incremental doses of 20, 50, 100 ug into the left coronary artery between March 2004 and April 2009. We compared the Ach provocation test results, its associated parameters, and 12-month clinical outcomes of cilostazol group (n=24) with those of non-cilostazol group (n=136). Results: The baseline clinical characteristics were similar between the two groups. Despite the expected results of improving endothelial dysfunction, after Ach injection, the rate of positive provocation test result (91.7% vs 66.2%, p<0.01) and diffuse spasm (91.7% vs 56.6%, p<0.01)were higher in cilostazol group. At 12 months, clinical outcomes including the rate of death, myocardial infarction, repeat revascularization and follow up CAG due to recurrent chest pain were similar between the two groups (Table). Conclusion: In our study, cilostazol may have significant impact on Ach-induced CAS in selective pts treated with DESs. However, cilostazol showed no significant impact on the clinical outcomes up to one year. Further study with larger study population and in selective pts without prior PCI with DES will be needed.