Acute lung injury (ALI), which is mainly triggered by infection, pneumonia, vasculitis, and sepsis, has no specific and effective therapy except for primary supportive treatment or bedside care. Excessive inflammation caused by innate immune cells is the major characteristic of ALI. Forsythoside B, a phenylethanoside compound, possesses good antioxidant and anti-bacterial properties in vivo and in vitro. In this study, the therapeutic potential of forsythoside B and its mechanism of action were investigated in a lipopolysaccharide (LPS)-induced ALI mouse model. The results showed that LPS-induced edema exudation and lung pathological changes in mice were significantly suppressed by forsythoside B pre-treatment. Furthermore, it also attenuated lung inflammation caused by LPS stimulation, evidenced by decreased inflammatory cell infiltration and down-regulated expression of cytokines, chemokines, and inducible enzymes. The anti-inflammation property of forsythoside B was confirmed in vitro using LPS-stimulated RAW 264.7 macrophages. Moreover, it alleviated LPS-induced inflammation by inhibiting the activation of TLR4/NF-κB signaling pathway in vivo and in vitro. In conclusion, the results demonstrated that forsythoside B protects against LPS-induced ALI by attenuating inflammatory cell infiltration and suppressing TLR4/NF-κB-mediated lung inflammation. Therefore, it might be a potential therapeutic agent for ALI caused by sepsis. Copyright © 2018 Elsevier B.V. All rights reserved.