Objective · To investigate the effect of the Toll-like receptor (TLR) nano-inhibitor P12 on THP-1 derived macrophages and acute lung injury (ALI) momodel inducedlipopolysaccharides (LPS). Methods · In in vitro experiments, THP-1 cells were differentiated into macrophage-like cells and then treated with LPS in the absence and presence of P12.After 24 h incubation, medium was collected to quantify the secretion of pro-inflammatory cytokines using enzyme-linked immunosorbent assay (ELISA). Six-to eight-week-old C57BL/6 mice were randomly divided into three groups, i.e. PBS control, LPS challenge and P12 pretreatment plus LPS. The bronchial alveolar lavage fluid (BALF) and lung tissue of each mowere collected, and the acute inflammatory response within lung was evaluatedtotal cell counts, differential cell counts and ELISA. Pathological injury scores in ALI mice were assessed with hematoxylin and eosin (H-E) staining of lung tissue sections under microscope. Results · In THP-1 derived macrophages, P12 significantly inhibited LPS-induced inflammatory cytokine production. In the LPS-induced ALI momodel, P12 significantly attenuated the acute inflammatory response and alveolar damage in lung, including reducing the number of total cells and neutrophils in BALF, decreasing the of chemokine production (KC and CCL-2), and lowering lung injury scores. Conclusion · P12 exhibits potent anti-inflammatory activity in THP-1 derived macrophages and in the LPS-induced ALI momodel, providing new concepts for the early treatment of ALI.