Abstract: Objective To study the effects of the age of mice first infected with respiratory syncytial virus (RSV) on Th17/Treg balance and airway inflammation during the second infection of RSV in adults. Methods Balb/c mice were divided into neonatal infection group and weaning infection group with 36 mice in each group. After twice RSV nasal drip, 6 mice were killed every other day at the eighth week. Lung tissue was taken , the percentage of Th17 and Treg cells was detected by flow cytometry , ELISA method was used to detect IL-17 concentration , Westernblot method was used to detect the expression of RORγt and FOXP3 protein. Results the percentage of Th17γt and foxp3 protein and the concentration of IL-17 in lung tissue of neonatal infection group were significantly higher than those of weaning infection group, while the percentage of Treg cell percentage of lung tissue was significantly lower than that of weaning infection group. The number of BALF cells, lymphocytes, neutrophils and eosinophils in neonate infection group was significantly higher than that in control group. Conclusion RSV infection in neonatal mice may aggravate Th17/Treg balance and airway inflammation in twice RSV infection adult mice.