Although Type 2 diabetes mellitus (T2DM) is a well-recognized risk factor for dementia, the neural mechanisms that underlie cognitive impairment in T2DM remain unclear. This study uses resting-state functional magnetic resonance imaging (fMRI) to examine attention network alterations in T2DM and their relationships to impaired cognitive performance. Data-driven independent component analysis was applied to resting-state fMRI data from 38 T2DM patients and 32 healthy controls to identify the dorsal attention network (DAN) and ventral attention network (VAN). Correlations were then determined among the resting-state functional connectivity (rsFC), clinical data, and neuropsychological scores. The T2DM patients exhibited decreased rsFC in the left middle frontal gyrus (MFG) and bilateral inferior parietal lobe (IPL) of the DAN, as well as the left IPL and right MFG/IFG of the VAN. In addition, the rsFC of the left MFG was inversely correlated with the Trail Making Test-B scores; the rsFC of the left IPL was positively correlated with the Digit Span Test scores but negatively correlated with HbA1c; and the rsFC in the right precuneus was positively associated with cognitive performance (without Bonferroni correction). In conclusion, T2DM affects resting-state attentional networks, which may be related to reduced attention and a hyperglycemic state.