Pulmonary fibrosis (PF) is a life-threatening non-tumorous disease characterized by progressive fibrosis and worsening lung function. Various drugs, such as bleomycin, can contribute to lung injury and PF, with lung injury potentially occurring in 10% of bleomycin users. Bleomycin is the most commonly used drug in the establishment of an animal model of PF in rats. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) serve an important role in controlling tissue organization and fibrosis following injury. The present study examined the effect of bosentan on fibrotic lung tissue in rats administrated with bleomycin. In total, 48 Wistar rats were administrated with bleomycin, with or without bosentan, while the control rats received saline. The lung tissues were microscopically examined by staining with hematoxylin and eosin and Masson's trichome. ELISA was also used to detect the MMP-9 and TIMP-1 concentrations in the plasma. The results indicated that the bosentan-treated groups on the next day and the 15th day showed significant reversal of pathological findings. In addition, the concentrations of MMP-9 and TIMP-1 appeared to be altered following bosentan treatment, improving the bleomycin-induced PF. Masson's trichome staining showed high collagen deposition in the lung tissue sections, which may be a direct result of the activity of MMP-9 and TIMP-1. Furthermore, the deposition of collagen was significantly inhibited in bosentan-treated groups. In conclusion, these results demonstrated that bosentan inhibited lung fibrosis induced by bleomycin and it may be used as an inhibitor of PF.