Background Retinopathy of prematurity (ROP) is one of major causes of childhood blindness.Early screening and treatment of ROP is necessary.Objective This study was to analyze the incidence of ROP in single and multiple premature infants and related factors.Methods This study was approved by Ethic Committee of Suzhou Municipal Hospital,and oral informed consent was obtained from the parents of the infants before any medical examinations.Five hundred and four fetus with the gestational age of ≤34 weeks or birth weight of ≤ 2 000 g were collected in Suzhou Municipal Hospital,of whom 357 infants were single fetus birth and 147 infants were multiple fetus,including 26 twins and 21 three fetus birth.The fundus were examined by RetCam Ⅱ equipment and ROP was determined based on the fundus findings and history of birth.ROP incidences between the single fetus and multiple fetus were compared,and the inducing factors were analyzed.Results Sixty-six infants were ROP in all 504 fetus,with the incidence of 13.10％.The incidence of ROP in the single fetal group was 10.92％ (39/357),which was significantly higher than 18.37％ (27/147) in the multifetal group (x2=5.069,P=0.024),and risk of ROP in the multifetal group was higher than that in the single fetal group (OR =1.835).The oxygen inhalation rate was 42.02％ (150/357) and the oxygen inhalation duration was 5.71 days in the single fetal group,and that in the multifetal group was 58.50％ (86/147) and 9.42 days,respectively.Conclusions Incidence and risk of ROP in the multifetal infants are higher than those in the single fetal infants,and low-birth-weight,less gestational weeks and excess oxygen inhalation are influence factors.