Aims: Patients with type 2 diabetes mellitus (T2DM) have reduced platelet inhibition compared with non-diabetics. The aim of this pilot study was to assess the functional impact of cilostazol or clopidogrel adding on standard aspirin and clopidogrel treatment in T2DM patients and coronay artery disease undergoing percutaneous coronary intervention(PCI). Methods:This was a prospective, double-blind, randomized, cross-over platelet function study. The cut-off value of clopidotrel resistance as expressed P2Y12 inhibition was below 20 % among patients with T2DM patients and coronay artery disease undergoing PCI. After PCI, T2DM patients on dual antiplatelet therapy were assigned to receive cilostazol 100 mg bid or clopidogrel 150mg for 28days and afterwards crossed-over treatment assignments for another 28 days. Platelet function test was performed at three time points: at baseline(T0), 28 days after randomization(T1), and 28 days after treatment cross-over(T2). The P2Y12 inhibition(%) determined through VerifyNow testing was analyzed. Results:A total of 34 T2DM patients were randomized into two groups (cilostazol adding vs clopidogrel doubling) ; 2 patients discontinued treatment due to side effects. The clopidogrel resistance expressed as P2Y12 inihbition was significantly improved following cilostazol treatment or clopidogrel doubling treatment compared with pretreatments and this effects continued after cross-over (figure 1. P2Y12 inhibition determined by the VerifyNow P2Y12 assay. P2Y12 inhibition values are expressed as percentage (%)). Conclusion:Adjunctive treatment with cilostazol in T2DM patients on standard dual antiplatelet therapy was strategy for overcoming clopidotrel resistance.