Objective To investigate the effects of total flavonoid fraction(TFF) from Nervilia fordii on lipopolysaccharide(LPS)-induced acute lung injury(ALI) in rats,and to explore their protective mechanism.Methods LPS-induced ALI model was established by LPS(5 mg/kg) injection via left cervical vein.Blood samples were collected from the cervical artery of all rats at 5 and 6 h after LPS challenge for arterial blood gas test and cytokines measurements,and pulmonary microvascular permeability(PMP),lung wet/dry weight ratio(W/D),and pathological features were observed.Results Phytochemical study showed that the TFF contained 67.3% of flavonoids expressed in rutin and three flavone glycosides.The TFF pretreatment(6.24 and 12.48 mg/kg) attenuated the partial arterial pressure of oxygen decline in blood significantly,and decreased the PMP and lung W/D in ALI rats.In addition,the TFF(6.24 and 12.48 mg/kg) also ameliorated the LPS-induced lung damages including alveolar edema,neutrophils infiltration,alveolar hemorrhage,and thickening of the alveolar wall.Furthermore,the treatment with the TFF(6.24 and 12.48 mg/kg) also down-regulated the levels of pro-inflammatory cytokines,such as tumor necrosis factor-α(TNF-α),interleukin-6(IL-6),and intercellular adhesion molecule-1(ICAM-1),and up-regulated the level of anti-inflammatory cytokine IL-10 in serum of ALI rats simultaneously.Conclusion These results suggest that the TFF could protect LPS-induced ALI in rats,which may be mediated,at least in part,by adjusting the production of inflammatory cytokines including TNF-α,IL-6,ICAM-1,and IL-10. Objective To investigate the effects of total flavonoid fraction (TFF) from Nervilia for dii on lipopolysaccharide (LPS) -induced acute lung injury (ALI) in rats, and to explore their protective mechanism. Methods LPS-induced ALI model was established by LPS (5 mg / kg) injected via left cervical vein. Blood samples were collected from the cervical artery of all rats at 5 and 6 h after LPS challenge for arterial blood gas test and cytokines measurements, and pulmonary microvascular permeability (PMP), lung wet / dry Results of Phytochemical study showed that the TFF contained 67.3% of flavonoids expressed in rutin and three flavone glycosides. The TFF pretreatment (6.24 and 12.48 mg / kg) attenuated the partial arterial pressure of oxygen decline in blood significantly, and decreased the PMP and lung W / D in ALI rats. In addition, the TFF (6.24 and 12.48 mg / kg) also ameliorated the LPS-induced lung damages including alveolar edema, neutrophils infiltration , of alveolar hemorrhage, and thickening of the alveolar wall. Futurertherm, the treatment with the TFF (6.24 and 12.48 mg / kg) also down-regulated the levels of pro-inflammatory cytokines, such as tumor necrosis factor- alpha (TNF- alpha) , interleukin-6 (IL-6), and intercellular adhesion molecule-1 (ICAM-1), and up-regulated the level of anti-inflammatory cytokine IL-10 in serum of ALI rats simultaneously. Conlusion These results suggest that the TFF could protect LPS-induced ALI in rats, which may be mediated, at least in part, by adjusting the production of inflammatory cytokines including TNF-α, IL-6, ICAM-1, and IL-10.