This paper proposes a method for evaluating endothelial function based on the dilation rate of an integrated air-cuff plethysmogram measured using an oscillometric approach. The method is not affected by blood pressure variations, and can be used to assess endothelial function quickly. In the study, the dilation rate of an integrated air-cuff plethysmogram was simulated to verify that the proposed method is suitable for evaluating arterial compliance changes related to endothelial function. The simulation results showed that changes in arterial viscoelastic characteristics can be assessed using the technique. Then, the proposed dilation rate for the integrated air-cuff plethysmogram and the value of percent flow-mediated vasodilation (%FMD) (a standard index used to evaluate endothelial function) were measured in the same subjects, with the results showing a significant correlation (r= 0.589) between the two. In addition, receiver operation characteristics (ROC) analysis was conducted to verify the method's effectiveness in determining the risk of arteriosclerosis. The results showed that the area under the curve (AUC) of the proposed index was 0.914, which was greater than or equal to the %FMD value. It was therefore concluded that the proposed method has potential for clinical use.