INTRODUCTION To investigate the associations between the insertion/deletion (I/D) polymorphisms in the angiotensin converting enzyme (ACE) gene and susceptibility to diabetic kidney disease (DKD); and the efficacy of valsartan in reducing the urine protein in Type 2 diabetes mellitus (T2DM) patients. MATERIALS AND METHODS We enrolled 128 T2DM patients in this study, including 54 cases with DKD (DKD+) and 74 controls (DKD-). The ACE polymorphism was assayed by polymerase chain reaction (PCR), and the genotype distribution and allele frequency were analyzed. The DKD+ group was subdivided into the DD, ID and II subgroups, based on their genotypes. In addition, patients with DKD received valsartan treatment for 12 weeks. We determined changes in the urinary albumin to creatinine ratio (ACR) and serum creatinine (SCr). RESULTS The frequencies of the genotypes DD and ID were higher in the DKD+ than in the DKD- group. The frequency of allele D was higher, and of allele I was lower, in the DKD+ than in DKD- group (p < 0.05). Following valsartan treatment, albuminuria was significantly decreased in subgroups DD and ID (p < 0.05). CONCLUSIONS In T2DM patients, the ACE I/D polymorphism was associated with onset of DKD. Furthermore, the ACE I/D polymorphism influenced the renoprotective response to valsartan: Patients with the DD genotype benefitted the most from this treatment.