Diabetes mellitus is one of the most common diseases in the world and can causemany types of neuropathies, and even mortality. It is therefore important to understand how diabetes mellitus alters the mechanical properties of nerve tissues and their blood vessels. In this study, in situ compression- and-hold circular compression tests were applied to the sciatic nerves of both diabetic rats and normal rats. Doppler optical coherence tomography (Doppler OCT) was then utilized to monitor the configuration of the arterioles in two groups of rats. The force data acquired in the compression tests were fitted by using Fung’s quasi-linear viscoelastic model (QLV) to determine the viscoelasticity of the nerves. The results show that the nerves in the diabetic group had a longer relaxation time than those in the normal group. Consequently, the Doppler OCT observations reveal that in contrast to the normal arterioles, the diabetic arterioles did not dilate in the relaxation phase. The results of the force data integrated with the corresponding arteriole dilatation images may explain why the diabetic patients are more prone to carpal tunnel syndrome. The results may facilitate developing new approaches for treating diabetic neuropathy and for nerve repair and regeneration.