Objective: To investigate the effect of pretreatment with Radix Paeoniae Rubra (RPR) on acute lung injury induced by intestinal ischemia/reperfusion in rats and its protective mechanism.Methods:n lung tissues was detected by immunohistochemistry and morphometry computer image analysis. Arterial blood gas analysis, lung permeability index, malondialdehyde (MDA) and superoxide dismutase (SOD) contents in lungs were measured. The histological changes of lung tissue were observed under light microscope.Results:The expression of HO-1 in RPR-pretreatment group and hemin group was obviously higher than that in sham-operation group and I/R group (P ＜ 0.01). The level of MDA and lung permeability index in RPR-pretreatment and hemin group were significantly lower than those in I/R group (P＜0.01 or P＜0.05), while the activity of SOD in RPR-pretreatment and hemin group was obviously higher than that in I/R group (P＜0.01 ). Under light microscope, the pathologic changes induced by I/R were significantly attenuated by RPR.Conclusion : Intestinal ischemia/reperfusion may result in acute lung injury and pretreatment with RPR injection can attenuate the injury. The protective effect of RPR on the acute lung injury is related to its property of inducing HO-1 expression and inhibiting lipid peroxidation.