Objective To investigate the expression of cystatin C(Cys C)and high-density lipopro-tein cholesterol(HDL-C)in the serum of patients with Alzheimer's disease(AD)and vascular dementia(VD),and their clinical application.Methods A total of 40 AD patients(AD group)and 40 VD patients(VD group)admitted to Jinhua Second Hospital from January 2020 to January 2022 were enrolled,and another 40 healthy individuals who taking physical examination in the hospital during the same period were subjected as control group.According to Montreal Cognitive Assessment Scale(MoCA)score,the AD patients were divided into mild(22 cases)and moderate to severe(18 cases)AD groups,and the VD patients were into mild(MoCA score 18-26,24 cases)and moderate to severe(MoCA score＜17,16 cases)VD group.Serum levels of Cys C and HDL-C were detected in all the participants,and the diagnostic efficacy of serum Cys C and HDL-C level for AD and VD was analyzed with ROC curve analysis.Results The serum levels of TC,TG,LDL-C and Cys C were significantly higher,and that of HDL-C was obviously lower in the AD and VD groups than the control group(P＜0.05).The Cys C level in the moderate to severe AD group and the moderate to severe VD group was higher than that in the mild AD group and the mild VD group(P＜0.05).There was no significant difference in HDL-C level among moder-ate to severe AD group,moderate to severe VD group,mild AD group and mild VD group(P＞0.05).The AUC value for the combined Cvs C and HDL-C for diagnosis of AD and VD were 0.980(95％CI:0.943-1.000)and 0.951(95％CI:0.905-0.996),respectively.Conclusion Detec-ting serum Cys C and HDL-C levels is simple and convenient.There are significant differences in their serum levels in the patients with AD and VD when compared with healthy population,which may become reference indicators for screening AD and VD.