Purpose : Coronary microvascular function is impaired in patients with diabetes. There has been few studies for the influence of chronic hyperglycemia on the pathogenesis of coronary microvascular dysfunction in diabetes. This study investigates whether chronic hyperglycemia and duration of diabetes affect the coronary microvascular integrity, by assessing the coronary flow velocities after successful percutaneous coronary intervention (PCI). Methods : Fifty-two lesions, in clinically indicative 42 patients (28 males and 14 females, mean age 58 짹 11) who received elective PCI, were studied. Using an intracoronary Doppler wire, coronary flow reserve (CFR) which was defined as the ratio of hyperemic to baseline peak velocity were measured after PCI. On admission, blood sample was acquired to evaluate the glucose level, glycated hemoglobin A1c (HbA1c) and total bilirubin, known as physiological antioxidant, without evidence of definitive liver disease. Results : The duration of diabetes was 8.6 짹 8.4 years and the mean values were glucose level 240 짹 86 mg/dL, HbA1c 8.1 짹 1.5 %, total bilirubin 0.58 짹 0.21 mg/dL and CFR 3.0 짹 1.3. In univariate analysis, diabetes duration (r=-0.305, p=0.0.35), the interaction between HbA1c and duration (r=-0.339, p=0.018) and serum total bilirubin (r=0.432, p=0.003) were significantly correlated with CFR. In the final model, the significant independent predictors of the coronary microvascular integrity were the interaction between HbA1c and duration and serum total bilirubin. Conclusions : These results suggest that chronic hyperglycemia and duration of diabetes and oxidative stress have a key role on the pathogenesis of the coronary microvascular dysfunction. Therefore, intensive glycemic control appears to be essential for preserve coronary microvascular integrity.