〔Abstract〕 Abstract Objective To explore the polymorphism of endothelial nitric oxide synthase (eNOS) gene in umbilical cord blood of preterm infants and its relationship with major complications in preterm infants . Methods A total of 254 preterm infants ( < 37 weeks) who were hospitalized were selected as the study subjects . Umbilical cord blood was collected at delivery to determine the genotypes and alleles of eNOS gene at three loci : rs61722009 , rs2070744 , and rs1799983 . Clinical data of the preterm infants were recorded , and the relationship between eNOS gene polymorphism and major complications in preterm infants was analyzed . Results ① The TC + CC genotype at locus rs2070744 was an independent risk factor for bronchopulmonary dysplasia (BPD) in preterm infants , with an OR (95% CI) of 1 . 266 ( 1 . 017 - 1 . 577) . ② The GT + TT genotype at locus rs1799983 was an independent risk factor for retinopathy prematurity (ROP) , with an OR (95% CI) of 1 . 184 ( 1 . 008 - 1 . 391) . ③ The AB + AA genotype at locus rs61722009 was also an independent risk factor for ROP , with an OR (95% CI) of 1 . 335(1 . 033 -1 . 726) . ④ There was no significant relationship between gene polymorphism and the occurrence of respiratory dis- tress syndrome (RDS) and periventricular-intraventricular hemorrhage (PIVH) . Conclusion eNOS gene polymor- phism is associated with the occurrence of BPD and ROP in preterm infants . The evaluation of eNOS gene polymor- phism by umbilical cord blood measurement is helpful for the prevention and correct management of some serious complications .