Objective To observe barrier function changes of gut mucosa in rats with acute respiratory distress syndrome(ARDS)．Methods Forty SD rats were randomized to an experiment group (n：30)and a control group(n=10)．Oleic acid was injected via vena femoralis to establish ARDS ratmode1．Subgroups in the experiment group were randomly divided by time 30 min，2 h，4 h interval after injection(n=10 in each subgroup)．Concentration of D-lactate and endotoxin and activity of diamineoxidase in blood plasma were measured．Histopathological changes of small intestine were observed under light microscope．Results Compared with the control group，the activation of diamine oxidase in the experiment group was higher after 30 min of injection(Plt;0.01)．Concentration of D-lactate，the activity ofdiamine oxidase and endotoxin level in the experiment group were all elevated after 2 hours of injection(all Plt;0.05)，and further elevated after 4 hours．In the rats’villous interstitial after 2 hours of the injection，there were edema，hyperemia，and infiltration of neutrophils，eosinophils and lymphocytes．After 4 hours ofthe injection，the villous epithelium showed desquamation，necrosis，denaturalization and erosion，associated with infihration of lymphocytes and neutrophils in the mucosa．Conclusion In oleic acid-induced ARDS．permeability of gut mueosa increases and gut barrier is dysfunctional．