Our study points out that the mechanism of CAT protecting against pulmonary fibrosis induced by BLM in mice is related to the regulation of TGF-β1, Smad2, Smad3, Ang II, AT1, E-cadherin, N-cadherin and α-SMA as well as the phosphorylation of Smad2 and Smad3, also it is given orally which makes it easier to put into clinical practice. This evidence concerns the gene AGT and pulmonary fibrosis.