With type 2 diabetes mellitus (DM2) as a concomitant disease, chronic cerebral ischemia (CCI) has a more severe course because of chronic hyperglycemia. Using resting state functional MRI (fMRI) data, this study aimed to investigate connectivity of cerebral neural networks in patients that have CCI with DM2 and without DM2. The study involved 257 CCI patients (81 male and 176 female, aged 50-85 years) some of whom had DM2. We assessed metabolic parameters, state of cerebral circulation, and cognitive functions. Resting fMRI was used for the analysis of structure of connectivity of cerebral neural networks. With false discovery rate (FDR) factored in, CCI patients with DM2 had values of some indicators of connectivity of cerebral neural networks at a level significantly lower than CCI patients without DM2 (p (FDR) < 0.05). Namely, the indicators in question were those of connectivity of right hemisphere's speech neural network, left hemisphere's parahippocampal region, and angular gyrus of the right hemisphere, which is an integral part of the brain's passive mode network. Also, CCI patients with DM2 had significantly poorer connectivity of anterior cingulate gyrus, part of the salient neural network, and superior temporal gyrus. There are significant changes in the cerebellar networks, too. Overall, the size and intensity of most of the neural networks studied in resting state are lower in CCI patients with DM2.