Abstract: AIM: To study the ultrastructure of dex-amethaone on the bleomycin induced pulmonary fibrosis.METHODS: Thirty Sprague-Dawley (SD) rats were ran-domly divided into three groups (n =10 in each):control group, bleomycin (BLM) group and dexamethasone (DXM) group.After 28 days, the MDA and SODof lung were measured and the histology was detected.RESULTS: In DXM group, the concentration of SOD was lower than that in the BLM group (P<0.01), and the degree of fibrosis was more mitigative than that in the BLM group by microscope and ultrastructure. CONCLUSION: Dexamethasone can reduce the damage of oxygen-derived free radicals of bleomycin.Treatment of dexam-ethasone may be useful in inhibiting pulmonary fibrosis.

Key words: dexamethasone, pulmonary fibrosis, oxygen-derived free radicals, ultrastructure