Abstract： Objective To observe the expression of tumor necrosis factor-α(TNF-α)in acute lung injury caused by paraquat(PQ)in rats,and investigate the mechanism of the rhubarb in respect of pmteetive effects.Method PQ intragastrically poisoning at the dose of 50 mg/kg made a model of the acute lung injury in Sprague-Dawley(SD)rats.Totally 144 adult healthy SD rats(72 female,72male)were randomly divided into control group (group A,n=24),poisoned group(group B,n=48),rhubarb treated group(group C,n=48)and the shaln poisoning group(group D,n=24).Rats of group B and group C were poisoned intmgastrically with PQ(50 mg/kg).and rats of group C and group D were intervened intragastrieally with 300 mg/(kg·d)of rhubarb in 15 min-utes.The white blood cells and total cells in bronchoalveolar lavage fluid(BALF)were counted by using a blood cell counting plate and the protein content of BALF was measured by using the way of Lowry in order to calculate the neutmphiks pereentage and lung permeability index.A small portion of left lung was stained with HE to observe the pathological changes and the expression oftumor necrosis factor-α in the rest of the left lung was observed with immunohistochemistry.The data were handled by the analysis of variance and NK method using SPSS 14.0.Re-suits Compared with group A,the lungs of rats mainly showed congestion,edema and leukocytes infiltration in group B,and fibrosis was found onlyt in a few rats.And the rate neutrophils percentage,protein content and lung permeability index in BALF increased(P＜0.01).The expression of TNF-α were obviously inereased at 12 hours after PQ poisoning,and immtmohistochemistry score (IHS)was higher,and peaked at 24 hours later(P＜0.05),then remained on a high level for a while and sluggishly declined.Compared with group B,the changes of above mentioned were alleviated obviously,and the expression of TNF-α delayed with the less magnitude of increasing an an obvious tendency of less expression.Compared with group B,delayed,lower increasing extent,obviously re-ducing tendency in group C with statistical difference in IHS(P＜0.05).Conclusions Rhubarb ameliorates a-cute lung injury caused by PQ poisoning in rats by means of inhibiting the expression of TNF-α in turn to alleviate inflammatory reaction.