Objective:To observe the effects of metformin treatment on urinary TNF-α in type 2 diabetic patients and explore its possible reno-protective mechanisms. Methods:A total of 121 of type 2 patients (the DM group) were divided into the insulin group and the sulfonylurea group,they were divided to 2 subpoups according to whether or not they received metformin (the INS-Ⅰ group,insulin only;the INS-Ⅱ group,insulin+metformin;the SU-Ⅰ group,sulfonylurea only;the SU-Ⅱ group,sulfonylurea metformin). Meanwhile,24 healthy subjects were selected as the normal control group (the NC group) so that FPG,PBG,HbA1c,duration,BMI,serum creatinine,urinary albumin/creatinine ratio (UACR) and urinary TNF-α/creatinine ratio (UTCR) were determined respectively between the NC group and the DM group and changes in them excretion were determined in subgroups. Results:1. In the DM group,the levels in FBG,PBG,HbA1c,UTCR and UACR were significantly higher than those in the NC Group. 2. Compared with the INS-Ⅰ group,UTCR and UACR in the INS-Ⅱ group were significantly decreased(P < 0.05);while compared with the SU-Ⅰ group,UTCR and UACR in the SU-Ⅱ group were significantly decreased (P < 0.05). 3. UTCR had significant positive correlation with UACR in patients with T2DM (r=0.73,P < 0.01). Conclusion:Metformin can reduce excretion of urinary TNF-α in type 2 diabetic patients,which may be associated with its renal protection.