Objective To study the impact of aging on the capability of regeneration and differentiation of lung stem cells in mice with bleomycin-induced pulmonary fibrosis． Methods The proportion of lung stem cells in mice after bleomycin treatment was analyzed by flow cytometry． The repair capability of lung stem cells in young and old mice was examined by immunohistochemistry and flow cytometry． Ｒesults The ratio of lung epithelial stem cells/lung total cells and lung mesenchymal stem cells/lung total cells were significantly decreased in the aged mice． The proliferating lung stem cells/lung total cells reduced in old mice during the repair process of bleomycin-induced pulmonary fibrosis． Conclusion The repair capability of lung stem cells during bleomycin-induced pulmonary fibrosis is decreased in aging．