Protein verification results showed that CHOP, TGF-β1, Smad3, α-SMA and apoptosis-related caspase-3 proteins were up-regulated in the model group compared with the normal group, suggesting that the pathogenesis of bleomycin-induced pulmonary fibrosis in mice is related to the regulation of endoplasmic reticulum stress pathways. Here, CASP3 is linked to pulmonary fibrosis.