To investigate the protective effect of genistein on endotoxin-induced acute lung injury in rats, and explore the underlying mechanisms, 32 male Sprague-Dawley rats were randomly divided into 4 experimental groups: saline control, genistein alone, lipopolysaccaride alone, and genistein pretreatment. Each treatment group consisted of eight animals. Animals were observed for 6 h after LPS challenge, and the wet/dry (W/D) weight ratio of the lung and bronchoalveolar lavage fluid(BALF) protein content were used as a measure of lung injury. Neutrophil recruitment and activation were evaluated by BALF cellularity and myeloperoxidase (MPO) activity. RT-PCR analysis was performed in lung tissue to assess gene expression of ICAM-1. The histopathological changes were also observed using the HE staining of lung tissue. Our results showed that lung injury parameters, including the wet/dry weight ratio and protein content in BALF, were significantly higher in the LPS alone group than in the saline control group (P＜0.01). In the LPS alone group, a larger number of neutrophils and greater MPO activity in cell-free BAL and lung homogenates were observed when compared with the saline control group (P＜0.01). There was a significant increase in lung ICAM-1 mRNA in response to LPS challenge (P＜ 0. 01, group L versus group S).Genistein pretreatment significantly attenuated LPS-induced changes in these indices. LPS caused extensive lung damage, which was also lessened after genistein pretreatment. All above-mentioned parameters in the genistein alone group were not significantly different from those of the saline control group. It is concluded that genistein pretreatment attenuated LPS-induced lung injury in rats.This beneficial effect of genistein may involves, in part, an inhibition of neutrophilic recruitment and activity, possibly through an inhibition of lung ICAM-1 expression.