Objective: To study the effect of Honokiol (HKL) on pulmonary microvascular endothelial cells in lipopolysaccharide (LPS) induced acute respiratory distress syndrome (ARDS) and its potential mechanism.Methods: Mouse lung microvascular endothelial cells (PMVEC) were cultured with DMEM+10%FBS in a six-well plate and divided into control group (Con group), Honokiol group (HKL group), Lipopolysaccharide treatment group (LPS group) and LPS+HKL treatment group (HKL+LPS group). The levels of Malondialdehyde and Reactive Oxygen Species in cell lysates were determined by TBARS assay kit and H2DCF-DA, respectively. TUNEL/DAPI double staining was used to detect apoptosis. The cell junction was detected by VE-cadherin/DAPI and Claudin-5/DAPI double staining. Western blotting was used to detect caspase-3, cleaved caspase-3, Sirt3, SOD2, and acetylated SOD2 (Ac-SOD2). 32 mice were randomly divided into control group (Con group), Honokiol group (HKL group), Lipopolysaccharide treatment group (LPS group) and LPS+HKL treatment group (HKL+LPS group). HE staining was used to observe the pathological changes of lung tissue.Results: Honokiol pretreatment could significantly reduce LPS-induced increase of ROS and MDA levels, and decrease LPS-induced increase of SOD2 acetylation and SIRT3 down-regulation. TUNEL and Caspase analysis showed that Honokiol could protect apoptosis of PMECs induced by LPS. VE-cadherin fluorescence staining demonstrate thag Honokiol pretreatment could prevent LPS from damaging cell adhesion. Claudin-5 fluorescence staining show that Honokiol pretreatment could prevent LPS from disrupting tight connections of cells. In animal experiments, HE staining showed that Honokiol significantly inhibited the typical pathological changes of ARDS in the lung tissue of mice in LPS group.Conclusion: HKL can significantly inhibit LPS-induced oxidative stress, apoptosis and cell connection breakdown of pulmonary microvascular endothelial cells, thereby alleviating ARDS symptoms.