Objective To investigate the association of serum Cystatin C level and mild cognitive impairment(MCI) in elderly people with type 2 diabetes mellitus(T2DM) and to analyze the risk factors for MCI. Methods A total of 156 elderly people with type 2 diabetes mellitus were divided into two groups: MCI and normal cognition(NC) group. All subjects were evaluated with cognition scores of Mini-mental state examination(MMSE), Montreal Cognitive Assessment(MoCA), Self-Rating Anxiety Scale(SAS), Center for Epidemiogical Studies Depression Scale(CES-D), Screening Scale for Parkinson disease (SSPD), Activity of Daily Living(ADL), and Global Deterioration Scale(GDS). CystatinC, HbA1c, triglyceride(TG), total cholesterol(TC), and blood pressure were examined. Independent t-test, correlations and logistic regression analysis were performed. Results The elderly diabetic patients complicated with MCI showed a higher level of serum Cystatin C than those in NC group (P=0.018). Cystatin C was negatively correlated with the score of MMSE, and score, visuospatial/executive, naming, attention, language and delayed recall of MOCA (P<0.001). Logistic regression analysis showed that diabetes duration, hypertension, HbA1c and Cystatin C were the variables of the equation. Conclusion Multiple risk factor including the higher level of serum Cystatin C may induce MCI in elderly T2DM people, but larger sample study is needed for further verification.