Objective To investigate the resting?state functional alteration in posterior cingulate cortex ( PCC) in Type 2 diabetes ( T2DM) patients with cognitive impairment and to determine the relation?ship of rs?fMRI changes with cognitive decline. Methods Resting?state functional magnetic resonance ima?ging was performed T2DM patients with impaired cognition ( n=19) and healthy control subjects ( n=20) . The amplitude of low frequency fluctuations ( ALFF) and regional homogeneity ( ReHo) values were calcu?lated in left PCC to represent the spontaneous brain activity. Using left PCC as a seed region,the functional connectivity of the whole brain was mapped. In addition,correlation analysis was conducted among ALFF,Re?Ho,and neuropsychological test scores. Results The ALFF values of left PCC (0.72±0.37) was decreased compared with the control group(1.09±0.46),but the ReHo value(1.12±0.10)was not significantly changed compared with control group (1.14±0.11). The functional connectivity was decreased with the left medial temporal lobe,left superior and middle temporal gyrus,right superior frontal gyrus,and right supplementary motor area ( SMA) ,while it was increased with the left middle frontal gyrus,inferior frontal gyrus and right cerebella. MoCA scores were positively correlated with the ALFF values of left PCC. Conclusion In resting state,the spontaneous activity and functional connectivity of PCC is altered in T2DM patients with cognitive impairement;and the function of PCC contributes to the cognitive decline associated with T2DM.The decrease of ALFF value of PCC may help to detect the cognitive decline of T2DM.