Background: Previous studies have shown that cilostazol may not only prevent stent thrombosis, but also may have positive effect in the prevention of restenosis. However, the effect of cilostazol on restenosis after successful deployment of drug-eluting stent (DES) in patients with diabetes mellitus was not evaluated. Methods and Results: A total of 280 patients at 8 clinical sites was randomized. The patients (61.7짹9.6 years old, males) who underwent successful stenting were randomized to aspirin and cilostazol (group I, n=141, 57.0짹9.4 years old) vs. aspirin and clopidogrel (group II, n=139, 63.0짹9.5 years old) after one month of aspirin, cilostazol, and clopidogrel combination treatment. The patients with group I were younger, male predominance, and much higher rate of current smoker. The types of DES implanted were not different between the groups (55 Cypher and 105 Taxus in group I vs. 52 Cypher and 108 Taxus in group II). There were no differences in angiographic and procedural characteristics between the groups. Major adverse cardiac events (MACE) including acute and subacute stent thrombosis within one month were not developed in both groups. Late stent thrombosis were 3 (1.9 %) in group I and 4 (2.5 %) in group II. Follow-up coronary angiogram was performed in 171 patients (53.4 %). The rate of angiographic restenosis (stent plus 5-mm borders) at the 6 month was 4 (5.7 %) in group I and 17 (16.8 %) in group II, p=0.03). The minimal luminal diameter at 6 months in group I patients was 2.91 mm compared with 2.69 mm in the group II patients. Major adverse cardiac events at 6 month were much lower in aspirin and cilostazol group. Conclusion: Our results demonstrated that the effect of combination therapy with aspirin and cilostazol for the prevention of stent restenosis were superior to those of aspirin and clopidogrel.