Abstract: Objective:To evaluate the clinical significance of serum cystatin C(Cys-C) level in patients with diabetes mellitus complicated with renal disfunction.Methods:The gender,age,course of disease,blood pressure,height and quality of 225 patients with diabetes mellitus were recorded,the body mass index(BMI) was calculated,and glomerular filtration rate(GFR)(mL·min^-1·1.73 m^-2) was detected using Kidney dynamic imaging.All patients were divided into the group A(GFR<60),group B(60 ≤ GFR<90) and group C(GFR ≥ 90).The levels of serum Cys-C,serum retinol binding protein(RBP),serum creatinine(Scr),blood urea(Sur),blood uric acid(UA),24 hour urine microalbumin(UmAlb) in three groups were detected.Results:The differences of the age,course of disease,and the levels of Scr,Sur,UA,RBP,Cys-C and UmAlb between three groups were statistically significant(P<0.05).The age,course of disease,and the levels of Scr,Sur,UA,RBP,Cys-C and UmAlb were negative correlation with GFR in three groups(P<0.01).The multiple stepwise regression analysis showed that the Cys-C,age,umalb entered the best equation,and serum Cys-C was the first.Conclusions:The Cys-C,age,UmAlb are the main influencing factors of GFR in patients with diabetes mellitus.The serum Cys-C is more ideal and sensitive conventional index in reflecting the early renal disfunction,which can help the early prevention and treatment of diabetic renal disease.