〔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 distress syndrome( RDS) and periventricular-intraventricular hemorrhage( PIVH).Conclusion e NOS gene polymorphism is associated with the occurrence of BPD and ROP in preterm infants. The evaluation of e NOS gene polymorphism by umbilical cord blood measurement is helpful for the prevention and correct management of some serious complications.