The aim of the present study was to evaluate the relationship of the manganese superoxide dismutase (MnSOD) Val16Ala (V16A) polymorphism with type 2 diabetes mellitus (T2DM) and diabetic nephropathy (DN) in Chinese patients, a case-control study was performed. This case-control study included 172 non-diabetic (non-DM) subjects and 257 T2DM patients with or without DN. Among T2DM patients, 154 had DN [albumin excretion rate (AER) >or= 30 mg/24 h] and 103 did not (AER < 30 mg/24 h), but the latter with known diabetes duration >or=10 years. The DN patients were further divided into groups with microalbuminuria (DN-1; n = 92; 300 > AER >or= 30 mg/24 h) and overt albuminuria nephropathy (DN-2; n = 62; AER >or= 300 mg/24 h). PCR-restriction fragment length polymorphism (RFLP) was used to detect genotypes of the V16A polymorphism for all subjects. The genotypic distributions of the V16A polymorphism in non-DM and T2DM subjects were in Hardy-Weinberg equilibrium and Ala allelic frequencies did not differ (11.9% vs. 9.1%; P > 0.05). The AA+VA genotypic frequencies of DN patients were significantly lower than those of non-DN patients (11.6% vs. 24.3%; P = 0.008). Multiple logistic regression analysis revealed that except for HbA1C, triglyceride, and BMI, which were high risk factors for the development of DN, the AA+VA genotype of the MnSOD-V16A polymorphism was an independent protective factor from the development of DN (odds ratio = 0.42; 95% CI = 0.18-0.95; P = 0.037) in T2DM patients. Our results suggested that the MnSOD-V16A polymorphism is associated with decreased risk of diabetic nephropathy in Chinese patients with type 2 diabetes.