Objective To observe the relationship between endothelial constitutive nitric oxide synthase (ecNOS) genetic polymorphism and diabetic retinopathy（DR）of non insulindependent diabetes mellitus (NIDDM) patients of the Han nationality.Methods A total of 166 patients who clinical diagnosed with NIDDM as case group, 85 cases of patients (cataract or fracture) and healthy subjects without diabetes, hypertension and kidney disease,over 40 years old of age and without consanguinity between each other were selected as normal control group. Case group were divided into non-DR (NDR) group, nonproliferative-DR (BDR) group and proliferativeDR (PDR) group according to the result of fundus fluorescein angiography. Case group and normal control group subjects all were Han nationality. DNA was extracted from peripheral venous blood; the fourth 27 base pairs (bp) repeat polymorphism of ecNOS gene by was measured by polymerase chain reaction (PCR). Results The 27 bp repeat sequences within the ecNOS gene present in the Han nationality,allele b repeat 5 times, alleles a repeat 4 times. PCR results showed that there are 2 alleles and 3 genotypes in normal control, NDR, BDR and PDR group. The frequency of genotype bb、ab、aa were 80%, 16.5%, 3.5% in normal subjects; 77.2％, 13.9%, 8.9％ in NDR group; 80.5％, 17.1%,2.4％ in BDR group;78.3％, 13%, 8.7％ in PDR group,respectively. The allele frequency (chi;2 =1.841) and gene frequency (chi;2=3.847) were not statistically significant (P＞0.5) in normal control,NDR,BDR and PDR group. Logistic regression analysis showed that there is no relation between DR and ecNOS duplicated gene polymorphism. Conclusions There is 27 bp repeated polymorphism in 4th intron of ecNOS gene, which may not be associated with the DR of NIDDM in the Han nationality.