Objective To investigate the role of cyclooxygenase-2 (COX-2) gene expression in TGF-β1-indcuedcollagen synthesis, transformation and Notch signaling in human fetal lung fibroblasts. Methods Human fetal lungfibroblasts MRC-5 cells transfected with non-targeting control or COX-2-specific siRNAs were treated with or without TGF-β1 for 48 h. Western blotting was used to detect COX-2 protein expression, alterations in the synthesis of COX-I and COXIII,and the EMT marker α-SMA, and changes in the expression of the Notch signal pathway receptor Notch1 and itscognate ligand Jagged1. Cell viability was assessed by CCK8 assay. Results COX-2 expression was significantly higher inthe TGF-β1 group than the control group. Transfection of cells with COX-2-specific siRNAs significantly attenuated TGF-β1-dependent induction of COX-2 expression ( P <0. 05), while transfection of cells with control siRNAs had no effect. Cellviability and the expression of COX-I, COX-III, α-SMA, Notch1 and Jagged1 proteins were significantly increased in theTGF-β1 group ( P <0. 05), when compared with the TGF-β1 group, but were suppressed following the transfection of cellswith COX-2 siRNA ( P <0. 05). Conclusions Inhibition of COX-2 gene expression may play a protective role in pulmonaryfibrosis by reducing lung fibroblast viability and suppressing the ability of these cells to synthesize collagen and activate Notch pathway signaling.