Endothelial cell myofibroblast transition (EndoMT) is found during the process of bleomycin (BLM)‐induced pulmonary fibrosis in rats, and plays a very important role in sustaining inflammation and collagen secretion. Moreover, some studies have suggested that the Notch1 signaling pathway may be involved in the expression of α‐smooth muscle actin (α‐SMA) in pulmonary microvascular endothelial cells (PMVECs), a protein marker of EndoMT. Therefore, we aimed to investigate the expression level of α‐SMA and Notch1‐related signaling molecules in PMVECs from BLM‐induced rats and determine the relationship between the Notch1 signaling pathway and the expression of α‐SMA in PMVECs. We found that the expression levels of α‐SMA, Notch1, and Jagged1 were upregulated, while the expression levels of Dll4 were downregulated. Furthermore, there was a positive correlation between the expression of Jagged1 and the α‐SMA proteins in PMVECs, and NF‐κB was downregulated by decreasing the expression of Jagged1. In conclusion, the Jagged1/Notch1 signaling pathway is activated in PMVECs during the pathogenesis of BLM‐induced pulmonary fibrosis in rats, and it may induce α‐SMA expression via a non‐canonical pathway involving NF‐κB as the target molecule. The precise mechanism and the molecules involved in this signaling pathway need to be further elucidated. The Jagged1/Notch1 signaling pathway is activated in PMVECs during the pathogenesis of BLM‐induced pulmonary fibrosis in rats, and it may induce α‐SMA expression via a non‐canonical pathway involving NF‐κB as the target molecule.