Background: Acute lung injury (ALI) is an inflammatory disorder. Semen Cassiae has potent anti-inflammatory activities. The aim of our study was to investigate whether Semen Cassiae plays a protective effect on lipopolysaccharide (LPS)-induced ALI and, if so, to elucidate its potential mechanism. Methods: Male Sprague-Dawley rat lungs were injured by intratracheal instillation of LPS. Rats were treated with Semen Cassiae or vehicle 3 h after LPS challenge. Samples were harvested 24 h post-LPS administration. We also investigated the effects of Semen Cassiae on LPS stimulation in RAW 264.7 cells. Results: LPS administration markedly induced pulmonary edema and polymorphonuclear neutrophil influxes. These changes were significantly attenuated in Semen Cassiae treated group. Moreover, Semen Cassiae markedly reduced pulmonary interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels. The pulmonary soluble epoxide hydrolase (sEH) activity and the DNA binding activity of Nuclear factor (NF)-kappa B were significantly inhibited in Semen Cassiae treated group. Furthermore, Semen Cassiae treatment significantly increased epoxyeicosatrienoic acids (EETs), and heme oxygenase-1 (HO-1) activity. Our in vitro study demonstrates that Semen Cassiae treatment may inhibit LPS induced I kappa B alpha phosphorylation and NF-kappa B p65 nucleus translocation. Conclusion: Semen Cassiae protects LPS-induced ALI in rats. Semen Cassiae can be developed as a novel treatment for ALI.