Abstract： Objective To investigate the relationship between diabetic retinopathy(DR)and insertion/deletion(a/b)polymorphism of a 27 base pair variable number tandem repeat(VNTR)in intron 4of the endothelial nitric oxide synthase(eNOS)gene.Methods 321 patients of type 2 diabetes mellitus with over 10 years duration(case group)and 146 normal subjects(control group)were enrolled in this study.All the clients are Han Chinese.The case group was divided into DR subgroup(1 54 patients)and non-DR (NDR)subgroup(167 patients)according to the results of indirect ophthalmoscope and fundus fluorescent angiography.The VNTR polymorphism in eNOS gene was determined by polymerase chain reaction(PCR)combined with 8% agarose gel electrophoresis.Then the b,a allele frequency and b/b.a/a.b/a allele frequency of two groups were compared,and its correlation with diseases were analyzed.Results The b allele frequency of the VNTR in intron 4 of eNOS gene in the DR group was significantly higher than that in the NDR group(χ2=4.745,P=0.029;OR=1.685,95% CI=1.050-3.905)and control group(χ2=6.958,P=0.008;OR=1.89l,95% CI=1.172-4.437);b/b allele frequency in the DR group was also significantly higher than that in the NDR group(χ2=4.811,P=0.028;OR=1.790,95% CI=1.060-4.645)and controI group(χ2=5.203,P=0.023;OR=1.859,95% CI=1.087-4.952).Conclusions The b allele and b/b genotype in intron 4 of eNOS gene in the Han Chinese are closely related to DR.