Abstract: Objective To evaluate the predictive value of serum microRNA-19a-3p (miR-19a-3p), microRNA-146a (miR-146a) and 25-hydroxyvitamin D₃ 25-(OH) D₃ for the prognosis of children with respiratory syncytial virus (RSV) bronchiolitis. Methods A total of 202 children with RSV bronchiolitis were enrolled as disease group, followed up for one year after discharge, and divided into good prognosis group (n=55) and poor prognosis group (n=147). Additionally, 180 healthy children matched by gender and age were selected as control group. Serum levels of miR-19a-3p, miR-146a and 25-(OH)D₃ were measured in both the disease and control groups. The clinical data and the levels of serum miR-19a-3p, miR-146a and 25-(OH)D₃ of children in the poor prognosis group and the good prognosis group were compared. The correlations of serum miR-19a-3p, miR-146a and 25-(OH)D₃ with the prognosis of children and their predictive value for poor prognosis of children were analyzed. Multivariate Logistic regression analysis was used to screen the related influencing factors of poor prognosis in children. Results The proportion of smoking among family members, the expression levels of serum miR-19a-3p and miR-146 in the poor prognosis group were significantly higher than those in the good prognosis group, and the level of 25-(OH)D₃ was significantly lower than that in the good prognosis group (P < 0.05). The expression levels of serum miR-19a-3p and miR-146a were positively correlated with the poor prognosis of the children (r=0.408, 0.332, P < 0.001), and the level of serum 25-(OH) D₃ was negatively correlated with the poor prognosis of the children (r=-0.386, P < 0.001). The results of receiver operating characteristic (ROC) curve analysis showed that the area under the curve (AUC) of serum miR-19a-3p, miR-146a and 25-(OH)D₃ for predicting poor prognosis in children was 0.726, 0.817 and 0.834, respectively. The AUC of the combined prediction of the three was 0.938, which was higher than that of the single prediction (Z=5.515, 3.879, 3.860, P < 0.001), and the sensitivity and specificity were 83.64% and 90.48%, respectively. The miR-19a-3p, miR-146a, 25-(OH)D₃ and smoking among family members were all influencing factors for the poor prognosis of children with RSV bronchiolitis (P < 0.05). Conclusion Serum miR-19a-3p, miR-146a and 25-(OH)D₃ all have certain predictive values for the prognosis of children with RSV bronchiolitis, and the combined predictive value of the three is higher.