Objective To investigate the incidence of retinopathy of prematurity (ROP) in extremely low birth weight infants and to explore their risk factors. Methods ROP screening was carried out in Shenzhen Eye Hospital from July 2006 to October 2011. One hundred and fortyfive infants with a birth weight less than 1000 grams were respectively analyzed. There were 93 males and 52 females. Their average gestational age was (28.5±2.0) weeks and average birth weight was (923.0±85.0) grams. The more advanced ROP stages during the follow up or between the 2 eyes of bilateral patients were recorded and analyzed in this study. All infants were first divided into ROP group or non-ROP group. All the ROP cases were further divided into mild ROP group and severe ROP group. Mild group included infants with stage 1, stage 2 and nonthreshold stage 3 ROP. Severe group included infants with pre-threshold type 1, threshold, aggressive posterior ROP and stage 4/5 ROP. Gestational age (less than or equal to 28 weeks or more than 28 weeks), birth weight (less than 750 grams or more than or equal to 750 grams), fetus number in one birth (single or multiple fetus), mode of delivery (normal or cesarean section delivery) and gender were analyzed as risk factors according to reference. SPSS 13.0 was used to do the statistical analysis. Results96/145 infants developed ROP with an incidence of 66.21%. There were 59 (40.69%) severe ROP infants who underwent laser coagulation, bevacizumab intravitreal injection or vitreoretinal surgery. The difference of gestational age, fetus number in one birth, mode of delivery between ROP group and non-ROP group was statistically significant (P＜0.05). The difference of gestational age between mild ROP group and severe ROP group was statistically significant (χ2=7.588,P=0.006).Logistic regression analysis showed that only gestational age related to ROP occurence［Exp（B）=0.328 07,P=0.005 19］. Conclusions The incidence of ROP and severe ROP are very high in extremely low birth weigh infants. ROP risk factors are various and mainly include gestational age less than or equal to 28 weeks, multiple fetus and normal delivery.