Objective To investigate the relationship between serum 25-hydroxyvitamin D3[25(OH)D3],red blood cell distribution width(RDW)and retinopathy of prematurity(ROP).Methods Children with ROP admitted to the hospital from May 2018 to May 2023 were selected as the study group(n=202),and 200 premature infants without ROP were selected as the control group(n=200).According to the degree of ROP lesions,the 202 children with ROP were divided into a mild group(n=109)and a severe group(n=93).The serum 25(OH)D3 and RDW levels of all subjects were detected.The receiver operating characteristic(ROC)curve was used to evaluate the evaluation value of serum 25(OH)D3 and RDW on the severity of ROP in chil-dren,and the influencing factors of the severity of ROP in children were analyzed by multivariate Logistic re-gression.Results The serum 25(OH)D3 level in the study group was significantly lower than that in the con-trol group,and the RDW level in the study group was higher than that in the control group,and the differenc-ese were statistiacally significant(P＜0.05).The serum 25(OH)D3 level in the severe group was significantly lower than that in the mild group,and the RDW level in the severe group was significantly higher than that in the mild group,and the differencese were statistiacally significant(P＜0.05).The area under the curve(AUC)of serum 25(OH)D3 and RDW for predicting the severity of ROP children were 0.754(95％CI:0.703-0.804)and 0.813(95％CI:0.768-0.862),respectively,and the AUC of the combined prediction of the two was 0.901(95％CI:0.853-0.947).There were statistically significant differences in birth weight and mechanical ventilation ratio between the mild group and the severe group(P＜0.05).Multivariate Logis-tic regression results showed that 25(OH)D3＜18.08 ng/mL(OR=3.251,95％CI:1.689-6.257),RDW≥69.41％(OR=3.691,95％CI:1.830-7.446)were risk factors affecting the severity of ROP children(P＜0.05).Conclusion The low expression of serum 25(OH)D3 and the high expression of RDW are closely related to the occurrence of ROP,and could be used as potential markers to evaluate the severity of ROP in children.