Abstract: Objective:To explore the value of serum cystatin C(Cys C) levels in determining the impairment of early renal function. Methods:Serum Cys C in 110 cases with renal function impairment was detected by an automated particle-enhanced turbidimetric immunoassay method,serum creatinine was determined by picricacid method and serum urea by urea enzymatic method,all of which were divided into 5 periods according to the level of glomerular filtration rate(eGFR),and the correlation analysis was carried out. Results:The serum level of Cys C increased with the decrease of the eGFR level in the 110 cases(P<0.01). The Cys C concentration levels had statistical meaning between the 5 periods(P<0.01). The abnormal detection in the 5 periods was 52.94%,64.29%, 92.00%,100.00% and 100.00%,respectively. The difference was significant(P<0.01). Conclusions:Serum Cys C is a sensitive indicator reflecting early renal damage,which is of great value in diagnosis of early renal diseases.