Background: M. Suaveolens Ledeb has long been used in China to treat inflammatory infectious diseases. Melilotus is extracted from Melilotus Suaveolens Ledeb and its therapeutic potential is associated with its anti-inflammatory activity. However, the precise mechanisms underlying its effects are unknown. This study was conducted to evaluate the protective effects of melilotus extract in a rat cecal ligation and puncture (CLP)-induced animal model of acute lung injury (ALI). Methods: A sepsis model was induced by CLP-like lung inflammation. Two hours prior to CLP administration, the treatment group was administered melilotus extract via oral injection. RT-PCR and Western blotting were used to test the expression of cannabinoid receptor (CB) 2, NF-kappa beta and I kappa beta from single peripheral blood mononuclear cells and lung tissues respectively. Enzyme linked immune sorbent assay was used to detect serum levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-10, and IL-12. The numbers of neutrophils, lymphocytes, macrophages and total cells in the bronchoalveolar lavage (BAL) fluid were counted. For histologic analysis, hematoxylin and eosin (H&E) stains were evaluated. Results: After inducing ALI by CLP for 24 hours, melilotus extract up-regulated peripheral blood mononuclear cell CB2 expression, blocked the activity of NF-kappa beta 65, and the number of neutrophils, lymphocytes and total cells were significantly lower in the melilotus extract group than the control group. In addition, TNF-alpha and IL-6 levels were significantly decreased in the melilotus extract group. Histological results demonstrated the attenuation effect of melilotus extract on CLP-induced lung inflammation. CB2 was negatively correlated to NF-kappa beta mRNA and proteins, respectively (r = -0.377, P < 0.05; r = -0.441, P < 0.05). Conclusion: The results of this study indicated melilotus extract significantly reduced CLP-induced lung inflammation by up-regulating CB2 expression. The remarkable protective effects of melilotus extract suggest its therapeutic potential in CLP induced-acute lung injury treatment.