Objective: This study will explore whether reactive oxygen species (ROS) is involved in TGF-β1-induced JNK activation, pulmonary fibroblast proliferation and collagen type I and III synthesis., Methods: Pulmonary fibroblasts were randomly divided into control (0.4% serum) and TGF-β1 (5 µg/L) groups to detect whether TGF-β1 could induce pulmonary fibroblast proliferation, synthesis of collagen I and III, phosphorylated-JNK (p-JNK) and 8-OHdG (indicator of ROS); while in the part to explore whether NAC (N-acetyl-L-cysteine, antioxidants) has the inhibitory role in TGF-β1-induced pulmonary fibroblast, it did control (0.4% serum), H2O2 (0.1 mmol/L, positive control), H2O2+NAC (10 mmol/L), TGF-β1 (5 µg/L), TGF-β1+NAC groups. Pulmonary fibroblast proliferation, 8-OHdG levels, expressions of JNK and collagen I and III were used by MTT assay, immunofluorescence and western blot respectively., Results: In the experiments to detect the effect of TGF-β1 on pulmonary fibroblasts, compared with control, TGF-β1 significantly stimulated pulmonary fibroblast proliferation and increased collagen I and III protein, p-JNK and 8-OHdG levels. In the next experiments to explore whether NAC has the inhibitory role in TGF-β1-induced pulmonary fibroblasts, compared with control, pulmonary fibroblast proliferation and the levels of collagen I and II, p-JNK, 8-OHdG were all significantly increased in H2O2 and TGF-β1 groups; while these changes were markedly blocked with the treatment of NAC., Conclusion: TGF-β1 induces pulmonary fibroblasts to generate ROS, which contributes to JNK activation and pulmonary fibroblast proliferation as well as collagen synthesis, while ROS inhibition suppresses this effet of TGF-β1 in pulmonary fibroblasts.