Objective:To investigate the influence of metformin on urinary albumin excretion,serum cystatin C and plasma homocysteine in patients with diabetic nephropathy. Methods:According to the levels of urinary albumin excretion,104 patients of type 2 diabetes mellitus were divided into non-albuminuria group(40 cases),microalbuminuria group(36 cases)and macroalbuminuria group(28 cases). Patients in each group were treated with insulin(INS subgroup)or insulin and metformin(INS+MET subgroup) so as to control FPG≤7 mmol/L and HbA1c≤7%. UAE,BMI,TG,TC,HDL-C,Cr,CysC and Hcy were measured before and after medication. 28 normal subjects were involved as control. Results:BMI,Hcy and TC were reduced and HDL-C was increased(P < 0.05) of whom had been medicated with metformin and insulin for 3 monthes. Cr,Ccr and CysC had no differences (P > 0.05)before and after the pharmacotherapy. Hcy was correlated independently with Cr and CysC(P < 0.05). Conclusion:Metformin had not showed an increase of nephropatic UAE and injuring effects to renal function. The decrease of Hcy by metformin showed beneficial effects on the renal function.