Abstract: Objective To investigate the association of the polymorphism of endothelial nitric oxide synthase (eNOS) 27 bp variable number of tandem repeats (VNTR) with diabetic nephropathy. Methods We examined 32 healthy controls and 84 cases with type 2 diabetes mellitus (DM). A 27 bp variable number of tandem repeats polymorphism of eNOS was identified by polymerase chain reaction (PCR). Fasting serum nitric oxide metabolites (NOx) of all the people were measured by nitrate reductase. DM patients were divided into three grouops according to UAER (DM1: UAER<20 μg/min ; DM2: UAER20~200 μg/min; DM3: UAER>200 μg/min). Results (1)The frequencies of allele a in all type 2 DM groups were significantly higher than that in control group. The frequencies of aa+ab genotype in all type 2 DM group were significantly higher than that in control group. The frequencies of allelea and aa+ab genotype in DM1 group were higher than that in DM2 and DM3 group. But the differences were not significant. (2) Fasting serum NOx in aa+ab genotype were significantly higher than that in bb genotype of control group. (3) Serum nitrites in DM1 was significantly higher than NC, but the NO levels of DM2 and DM3 were significantly lower than NC group. (4) The albumin excretion ratio and serum creatinine level in aa+ab genotype were significantly higher than that in bb genotype of DM group. Conclusion The polymorphism of eNOS gene 27 bp VNTR is associated with diabetic nephropathy. These results support that allele a of the eNOS gene would be a clinically useful genetic marker for predicting the development of diabetic nephropathy.