Abstract： Objective To explore the diagnostic value of cystatin C(CysC) on early kidney damage in primary hypertension. Method To detect the CysC, BUN, Scr, UA in Ⅰ (31), Ⅱ (31), Ⅲ (31) stage of primary hypertension patients and 40 control cases ,then compared these results with normal control. Results The level of CysC in serum of Ⅰ , Ⅱ, Ⅲ stage of primary hypertension was(0. 81 ± 0. 16), (0. 94 ± 0. 23), (1.19 ± 0. 46) mmg/L, all of them were higher than normal control (0. 75 ± 0. 10) mg/L. The difference of CysC between Ⅱ、Ⅲ stage of primary hypertension and normal control was significant (t = 4. 195, t = 4. 446, P ＜ 0.01). The level of CysC in Ⅲ stage of primary hypertension was higher than in Ⅰ , Ⅱ stage(t = 4. 382 ,t = 4. 250,P ＜ 0.01). Significant positive correlation was observed between CysC and Scr(r = 0. 713,P＜0.01) ,CysC and UA(r=0. 45,P ＜0.01). Conclusion Serum CysC was a sensitive and reliable indicator on early kidney function damage in primary hypertension.