Vascular endothelial dysfunction is well known as an early symptom of atherosclerosis, and therefore simple and quantitative assessment of vascular endothelial function is required for early detection of the atherosclerosis. Our research group has developed a novel non-invasive technique for assessment of vascular endothelial function by using the oscillometric method, which is called the enclosed zone flow-mediated dilation (ezFMD). This paper introduces the measuring principle and the protocol of the ezFMD with assessment examples of vascular endothelial function.