Respiratory syncytial virus(RSV)is a leading cause of lower respiratory tract disease. The major high risk population for RSV infection are<6month infants and elders with age older than 65 years. At present, BALB/c mice were wildly used as animal model for RSV infection, however there has no report about the comparison of different week-ages BALB/c mice after RSV infection. A different week-ages BALB/c mice model was described in this study to compare their susceptibility after RSV infection. Young(10weeks),middle aged(30weeks)and aged(60weeks)mice were intranasally infected with 106 or 107plaque-forming units (PFU) RSV, then clinical symptom, weight, RSV titer in nose/lung, histology and immunohistochemistry was examined. And age-related susceptibility was analyzed. A high-titer virus(107PFU)infection showed significant weight loss at 6-11 day post infection while 106 PFU didn’t lead to obvious weight change. In 10(7) PFU infected group, replication of virus in nose and lung was detected, the virus in lung located around pulmonary alveoli, and the hematoxylin eosin stain showed significant infiltration of inflammatory cells and pathological tissue damage. Mice trended to be more susceptible to RSV infection as the growth of age. Older mice experience more weight loss. Lung histology of older mice showed more serious bronchiolitis and increased number of inflammatory cells in alveolar spaced, and 60week-old mice tended to be the most significant. In this study, we have successfully established a different week-ages BALB/c mice model, which will serve as the basis for investigating antibody or vaccine and further infection mechanism research of RSV.