Abstract: Objective To investigate the changes and clinical value of serum cystain C (CysC) in patients with early diabetic nephropathy (DN). Methods According to the urine trace albumin excretion rate (UAER), 120 Type 2 diabetic (T2DM) patients were divided into DM without albuminuria （UAER<30mg/24h, 60 cases) group and DM with microalbuminuria （UAER30-300mg/24h, 60 cases) group. The serum CysC, BUN and serum creatinine in T2DM and health controls were detected by using immune turbidimetric, Immunization rate and enzymatic determination respectively. Results The abnormal detection results of serum CysC, BUN and Scr in 60 T2DM patients with microalbuminuria were 80.0%, 10.0% and 18.3% separately. The abnormal results rate of CysC was apparently higher than that of BUN and Scr. Conclusion Serum CysC concentrations could be used as the early diagnosis index in T2DN, and also will share great clinical significance in detecting the degree of kidney damage.