Abstract: AIM: To explore the effect of insulin treatment on coronary perfusion and atherosclerosis plaque. METHODS: A total of 62 patients with type II diabetes mellitus and coronary artery disease (CAD) underwent coronary angiography (CA) and intravascular ultrasound (IVUS) tests. Patients were divided into two groups according to insulin injection. We compared corrected TIMI frame counts (CTFC) and IVUS morphologic status between groups. RESULTS: There was no difference between groups in terms of plaque volume, morphology and composition. CTFC were less in insulin group regardless of gender and vessels (P<0.05). CONCLUSION: Insulin treatment improves coronary perfusion by improvement of endothelial cell function but has no positive effect on well-formed atherosclerosis plaques.