Abstract: Objective To compare the changes of endothelial function in type 2 diabetic patients with atherosclerosis (AS) after treatment with angiotensin-coverting enzyme inhibitor (ACEI) and angiotensinⅡreceptor blocker (ARB). Methods Totally 145 type 2 diabetic patients with AS were included in this study. According to completely randomized open unbalanced design, the patients were assigned into ACEI group (n=99) with ramipril treatment (starting dose of 2.5 mg/d and gradually reaching 5 mg/d), ARB group (n=25) with irbesartan treatment (with gradual increase of doses till reaching the maximum daily dose of 150 mg), and control group (n=21) without the above medication. After a treatment lasting for 3 months, the brachial artery endothelial function was evaluated with two-dimensional ultrasonography. Results and Conclusions After therapy, endothelium-dependent vasodilation (EDV) of the brachial artery increased from (3.55±2.80)% to (5.62±4.18)% (P=0.001), and endothelium-independent vasodilation (EIV) increased from (12.62±7.48)% to (12.80±7.04)% (P=0.835) in ACEI group. EDV increased from (4.42±2.95) % to (6.28±3.26)% (P=0.039), while EIV decreased from (10.69±5.85)% to (9.54±4.78)% (P=0.229) in ARB group. No statistical changes in the indices were found after therapy in the control group (P>0.05). Comparison of endothelial function in the 3 groups showed no statistical significance in the changes of EDV between ACEI and ARB groups (P=0.853). No differences were found in the change of EIV in the 3 groups (P=0.644). The therapy with 150 mg irbesartan and 5 mg ramipril for 3 months produces similar effects on the endothelial function in these patients.