This study aims to investigate brain microstructural changes in white-matter and gray-matter of type 2 diabetes mellitus(T2DM) patients using the NODDI model. Thirty-three T2DM patients were divided into two sub-groups (impaired and normal cognition), together with ten healthy controls, were imaged at a 3T scanner. It was found that the T2DM patients with cognitive impairment had a lower ICVF value compared to healthy controls in WM regions and the thalamus. Decreased ICVF values in the genu of corpus callosum were correlated with HbA1c level. The NODDI model shows potential feasibility in characterizing brain microstructural alterations for patients with T2DM.