AIM:To investigate the effects of Auricularia auricular-judae polysaccharide ( AAP) on pulmonary tissues of rats with LPS-induced acute lung injury (ALI) and its mechanisms.METHODS: Adult Sprague-Dawley rats were randomly divided into control group , LPS group, low-dose AAP group, middle-dose AAP group, high-dose APP group, and dexamethasone group.The rats were injected with LPS (8 mg/kg, ip) to induce ALI.The rats in the AAP groups were treated with AAP for 7 d before the induction of ALI .The protein concentration in the bronchoalveolar lavage fluid (BALF) was measured.The lung edema degree was measured by detecting the wet /dry weight ratio.The myeloper-oxidase ( MPO) , total antioxidant capacity ( T-AOC) , total superoxide dismutase ( T-SOD) , nitric oxide synthase ( NOS) and malondialdehyde ( MDA) levels were determined .The pathological changes of the lung tissues were evaluated by HE staining.RESULTS:Treatment with AAP significantly improved LPS-induced lung pathological changes , attenuated the protein concentration in the BALF and wet/dry weight ratio , inhibited the activities of MPO and NOS , reduced MDA level and increased the activities of T-AOC and T-SOD.CONCLUSION: AAP protects against LPS-induced acute lung injury in rats.