Abstract: Objective：To observe the relationship between serum Klotho levels and the progression of renal function in patients with chronic kidney disease (CKD)and investigate further the feasibility of serum Klotho levels for predicting the progression of renal function in CKD patients. Methods：Eighty-one nondialysis patients with CKD 3 to 5 stages and 30 healthy volunteers in the First People′s Hospital of Kunshan were enrolled for a 12 months of followup. The levels of Klotho and fibroblast growth factor 23 (FGF23)in serum were detected by ELISA at the beginning and the end of the followup. The other related indicators were also tested simultaneously. GFR values were calculated by MDRD and GC formulas. According to the decreasing range of GFR, the CKD patients were subdivided into two groups: deterioration group and stability group for renal function, and the relationships between Klotho levels and progression of kidney function were evaluated. Results：The patients were followed up for an average of (9.5±2.9)months. GFR in CKD patients decreased from (24.8±12.4)mL/min to (18.7±12.1)mL/min (P＜0.01), and serum Klotho level decreased from 2.53 (1.41, 3.67)ng/mL to 1.63 (1.07, 3.19)ng/mL (P＜0.01)with more pronounced trend in the patients with renal function deterioration than the patients in stability group (P＜0.01). Fifteen patients with high Klotho level suffered from adverse kidney outcomes while 26 ones with lower Klotho level suffered from deterioration of renal function (63.4% vs 36.5%, P=0.02). KaplanMeier analysis revealed the high risk of adverse kidney outcomes arose in the CKD patients with lower Klotho level (P=0.013). Conclusion：Klotho level in CKD patients may significantly decrease and should be more apparent with renal function progresses. Lower Klotho level in serum may be associated with high risk of adverse kidney outcomes and become a promising marker to predict CKD progression.