Abstract： Objective To investigate the time and risk factors for spontaneous closure of patent ductus arteriosus (PDA) in preterm infants. Methods One hundred and seventy-seven preterm infants with arterial ductus unclosed were divided into three groups according to their gestational age as 28-31+6 weeks group (n=44),32-34+6 weeks group (n=59) and 35-36+6 weeks group (n=74).PDA was diagnosed by echocardiography in time of ≤12 h,-24 h,-48 h,-72 h,-96 h,-120 h,-144 h and ＞144 but ≤168 h after birth.The parameters of cardiac function included peak flow rate of aorta valve orifice,peak flow rate of pulmonary artery valve orifice,cardiac output,stroke volume,ejection fraction,the ratio of early (E) and late (A) diastolic velocities of mitral and tricuspid valves.The risk factors of arterial ductus spontaneous closure were determined by Logistic regression analysis.Results The cumulative spontaneous closure rates of preterm infants in three groups were 95.5％,100.0％ and 100.0％ within 168 h after birth respectively. There were significant differences of cumulative spontaneous closure rate in different time among three groups (x2 =4.23,7.45,12.46,7.14,4.75,6.47,3.89 and 3.89 respectively,P＜0.05).After spontaneous closure of PDA during 12-24 h, peak flow rate of pulmonary artery valve orifice increased [(0.69±0.12) cm/s vs (0.65±0.12) cm/s,t=2.37,P=0.02],peak flow rate of aorta valve orifice [(0.65±0.11) cm/s vs (0.69±0.12) cm/s,t=2.51,P=0.02] and ejection fraction [(63.00±8.50) ％ vs (66.00±8.50) ％,t=2.34,P=0.02] decreased.Logistic regression analysis showed that,the risk factors of preterm infants with arterial ductus unclosed within 24 hours after birth were gestation age (OR =1,825,95％CI:1.239-2.689),1 min Apgar score 0-3 (OR=1.946,95％CI:1.572-3.527) and early onset sepsis (OR=3.215,95％CI:1.245-5.463) ; gestation age (OR=3.270,95％CI:1.852-5.774),twins (OR=3.634,95％CI:1.489-8.871),1 min Apgar score 0-3 (OR=3.752,95％CI:2.156-5.436),Ⅲ-Ⅳ stage of respiratory distress syndrome (OR=2.897,95％CI:1.764-5.348) and early onset sepsis (OR=3.172,95％CI:2.134-6.437) were the risk factors of preterm infants with arterial ductus unclosed during 24-48 hours after birth; and gestational age (OR=2.471,95％CI:1.087-5.613),1 min Apgar score 0-3 (OR=2.985,95％CI: 1.469-5.736), Ⅲ-Ⅳ stage of respiratory distress syndrome (OR =3.645,95％ CI:1.879-6.282),fluid volume excess (OR =4.135,95％CI:2.146-7.428) and early onset sepsis (OR=3.246,95％CI:2.146-4.526) for those with arterial ductus unclosed during 48-72 hours after birth. Conclusions The spontaneous closure rate of arterial ductus in the newborn infants whose gestational age over 28 weeks was above 90％ in the first week after birth.There was no difference of left ventricular pump function between before and after the spontaneous closure.Reducing the incidence of premature birth,twins,severe asphyxia,severe respiratory distress syndrome, fluid excess and early onset sepsis might improve the spontaneous closure of arterial ductus.