〔Abstract〕 Objective　To investigate the role of runt-related transcription factor 3 （RUNX3） in transforming growth factor-β1 （TGF-β1）-induced activation of mouse primary pulmonary fibroblasts （PFs）， and its effects on fibroblast activation protein （FAP） expression， cell proliferation， and collagen synthesis.Methods　PFs were isolated from C57BL/6 mice and cultured. A RUNX3 knockdown model was established using small interfering RNA （siRNA）. Cells were assigned to the control group （Control）， TGF-β1-treated group （TGF-β1）， negative control group （TGF-β1+siRNA-NC）， and RUNX3-silenced group （TGF-β1+si-RUNX3）. In addition， a RUNX3 overexpression rescue experiment was performed based on TGF-β1 stimulation. Protein and mRNA levels of RUNX3， FAP， and typeⅠcollagen （COL1A1） were measured by Western blot and reverse transcription quantitative real-time PCR （RT-qPCR）. Cell proliferation was assessed using CCK-8 and EdU assays. Co-expression of COL1A1 and FAP was examined by double immunofluorescence staining.Results　Compared with the Control group，RUNX3， FAP， and COL1A1 expression levels were upregulated in PFs in the TGF-β1 group （P<0. 01）. The CCK-8 assay showed that the absorbance value was reduced in the RUNX3 knockdown group compared with the negative control group（ P<0. 01）. Consistently， the EdU assay demonstrated a lower proportion of EdU-positive cells in the RUNX3 knockdown group than in the negative control group （P<0. 01）. Immunofluorescence double staining re‑vealed decreased fluorescence intensities of COL1A1 and FAP in the RUNX3 knockdown group relative to the nega‑tive control. Under RUNX3 overexpression conditions， these fluorescence signals exhibited a partial rebound（ P<0. 01）. Conclusion　 RUNX3 in TGF- β1-induced PFs may promote cell proliferation and collagen synthesis by positively regulating FAP expression. Targeting the RUNX3/FAP axis may represent a potential therapeutic strat‑egy for pulmonary fibrosis.