Background: Pulmonary fibrosis (PF) is a fatal disease with increasing incidence. Ligustilide (LIG) has been shown to inhibit oxidative stress, apoptosis, and inflammation. Here we investigated the possible effect of LIG on bleomycin-induced PF in Sprague-Dawley rats.Methods: PF rats were set up through a single endotracheal injection of bleomycin (5 mg/kg). Then rats were treated with 20, 40, and 80 mg/kg LIG for four weeks, and the effects were estimated.Results: Overall, LIG significantly improved ventilation and reduced hyperplasia, and treatment of LIG reduced fibrosis as indicated by Masson staining and reduced expression of transforming growth factorbeta (TGF-β), Fibronectin, and alpha-smooth muscle actin (α-SMA). Oxidative stress was induced with bleomycin while inhibited with LIG, as showed with rebalanced serum lactate dehydrogenase (LDH), and tissue superoxide dismutase (SOD), glutathione peroxidase (GSH) and malondialdehyde (MDA). Apoptosis was further inhibited with LIG, as shown with Terminal dUTP nick-end labeling (TUNEL) staining and expression of Caspase-3, Caspase-9, Bax, and Bcl-2. Th1/Th2 balance was also rebuilt as evaluated with CD4 and IFNγ/IL-4 labeled flow cytometry of peripheral blood mononuclear cells (PBMCs) and expression of inducible nitric oxide synthase (iNOS) and IL-10 in the serum and lung. Protein expression of Toll-like receptor 4 (TLR4), HSP60-TLR4-myeloid differentiation factor 88 (Myd88) and nuclear factor-kappa B (NF-κB) p-P65/P65 was significantly reduced with LIG treatment. All the effects of LIG exhibited in a dosedependent way.Conclusions: LIG improved bleomycin-induced PF with improved ventilation, reduced fibroblast, reduced oxidative stress and apoptosis, and rebalanced Th1/Th2 immunity, through TLR4/MyD88/NF-κB P65 signaling.