Objective To confirm epithelialmesenchymal transition(EMT) and the expression of osteopontin (OPN) in various periods of mice BLMinduced pulmonary fibrosis by semiquantitative analysis and pathomorphological evaluation. Methods sixty healthy adult male C57BL/6 mice were randomly divided into the NS-Control group and the BLMinjured group，which were treated with 50μl NS and 50μl BLM solution by oropharyngeal aspiration respectively. Left lung tissues were taken from all the mice and paraffin imbedding and section were performed separately on days 3,7,14,21,28 after the treatment. The histopathological changes and total lung collagen content of mice were determined by hematoxylineosin staining and sirius red staining. The expressions of OPN,SP-C,E-Cadherin、FSP1 and vimentin were detected by immunohistochemical staining. Integrated absorbance(IA)of stained sections was measured by ImagePro Plus 6.0, and then the statistical analysis was done. Results The morphological changes of mice lung tissue in various periods were demonstrated by HE staining. Total lung collagen content of BLMgroup increased during the pulmonary fibrosis progress by picrosiriuspolarization staining (P<0.05) In immunohistochemical staining, the expression of OPN in the BLMgroup was more significant than that in the NSgroup, peaking on day 21-28; lots of SP-C positive typeⅡalveolar cell of normal size were observed in the NSgroup, and a progressive amount of positive cells in the fibrous focal zone with bigger cell body was seen in the BLMgroup; a few of E- Cadherin positive alveolar epithelial cells could be seen in the NStreated lung and 14-day and 21-day BLMinjured