Objective:To observe the effect of hydroxysafflor yellow A (HSYA),an active ingredient of a traditional Chinese herbal medicine Carthamus tinctorius L.,on lung inflammation and pulmonary fibrosis induced by bleomycin (BLM) in rats.Methods:Animals were divided into 6 groups including normal group,model group,three HSYA groups and dexamethasone (DXM) group.Three doses of HSYA (35.6,53.3,and 80.0 mg·kg-1·day-1)were intrapedtoneally (i.p.) injected in rats for 3 weeks after BLM administration and DXM was used as the positive control (n=8 or 12).Arterial blood gas was assayed and morphological changes were observed.Lung mRNA expressions of tumor necrosis factor (TNF)-α,intedeukin (IL)-1 β,IL-6 and some cytokines in lung tissue were detected by real-time polymerase chain reaction.Nuclear factor-κ B p65 or α-smooth muscle actin (α-SMA)protein distribution in rat lung tissue was observed by immunohistochemistry.Results:On the 7th day after BLM administration,lung tissue showed serious inflammation.Treatment with HSYA or DXM ameliorated lung inflammation.After treatment with HSYA or DXM,oxygen partial pressure (PaO2) increased (HSYA 80.0 mg·kg-1,P＜0.01) and CO2 partial pressure (PaCO2) decreased (HSYA 53.3,80.0 mgokg-1,P＜0.05).Moreover,the mRNA expression of TNF-α,IL-1 β,and IL-6;and the number of NF-K B p65 positive cells was lower in HSYA 53.3 and 80.0 mg·kg-1 groups than those in the model group (all P＜0.05).Twenty-one days after BLM administration,HSYA or DXM treatment ameliorated fibrosis,increased PaO2 (HSYA 53.3,80.0 mg·kg-1,P＜0.01),and decreased PaCO2 (53.3 and 80.0 mg·kg-1,P＜0.05).Further,the mRNA expression of TGF-β 1,α-SMA,and collagen Ⅰ as well as the number of α-SMA positive cells increased in the model group and HSYA can attenuate these changes (53.3,80.0 mg·kg-1,P＜0.05).Hematoxylin and eosin and Masson\'s tdchrome staining indicated that the fibrosis and collagen deposition were ameliorated in HSYA groups (53.3,80.0 mg·kg-1,P＜0.05).Conclusion:HSYA could alleviate acute lung inflammation and chronic pulmonary fibrosis induced by BLM in rats.