Background Gefitinib, an inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, is an effective treatment for epithelial tumors, including non-small cell lung cancer (NSCLC), and is generally well tolerated.However, some clinical trials revealed that gefitinib exposure caused lung fibrosis, a severe adverse reaction.This study investigated the effect of gefitinib on lung fibrosis in mice.Methods We generated a mouse model of lung fibrosis induced by bleomycin to investigate the fibrotic effect of gefitinib.C57BL/6 mice were injected intratracheally with bleomycin or saline, with intragastric administration of gefitinib or saline.Lung tissues were harvested on day 14 or 21 for histology and genetic analysis.Results The histological results showed that bleomycin successfully induced lung fibrosis in mice, and gefitinib prevented lung fibrosis and suppressed the proliferation of S100A4-positive fibroblast cells.In addition, Western blotting analysis revealed that gefitinib decreased the expression of phosphorylated EGFR (p-EGFR).Furthermore, quantitative real-time PCR (qRT-PCR) demonstrated that gefitinib inhibited the accumulation of collagens Ⅰ and Ⅲ.Conclusions These results reveal that gefitinib reduces pulmonary fibrosis induced by bleomycin in mice and suggest that administration of small molecule EGFR tyrosine kinase inhibitors has the potential to prevent pulmonary fibrosis by inhibiting the proliferation of mesenchymal cells, and that targeting tyrosine kinase receptors might be useful for the treatment of pulmonary fibrosis in humans.