Myofibroblast plays an important role in the progression of pulmonary fibrosis, featured by the presence of α-smooth muscle actin (α-SMA). It has been a novel therapeutic target. Safflor yellow (SY) is extracted from safflower, a traditional Chinese medicine. The aim of our study is to investigate the effects of SY on rats of pulmonary fibrosis induced by bleomycin (BLM) and on differentiation of lung fibroblast into myofibroblast stimulated by transforming growth factor-β1 (TGF-β1). Two dose SY (intraperitoneal, 25, 50 mg/kg/d) were administered to rats treated by BLM consecutively for four weeks. It was found that SY alleviated the loss in body weight, the increase of hydroxyproline content in the lung tissues and pathologic changes of pulmonary fibrosis caused by BLM instillation. SY also prevented the increase of α-SMA positive cells and TGF-β1 expression induced by BLM. These effects were more significant when treatment with high-dose SY. Moreover, SY (0.05, 0.25, 1.25 mg/ml) inhibited the expression of α-SMA during differentiation of lung fibroblast into myofibroblast stimulated by TGF-β1. SY had anti-fibrotic effect in experiment and might be employed as a therapeutic candidate agent for attenuating pulmonary fibrosis.