Objective To investigate the effects and mechanisms of bile on small intestine mucosal barrier.Methods Fifty Wistar rats were assinged into 3 groups randomly: obstructive jaundice (OJ) group （n=20）, biliary external drainage group （n=20） and control group （n=10）. Ten days after operation, the plasma endotoxin level was determinated, the terminal ileum mucosas was obtained to be morphologically measured by light microscope, and immunohistochemistry and Western blot were uesd to examine the expressions of tight junction proteins zona occludens-1 (ZO-1) and occludin in the mucosas. Results Atrophy significantly appeared in the distal ileum mucosas in OJ group. Compared with control group, the intestinal villus height, mucosa thickness and crypt depth in OJ group were obviously decreased 27.8%, 21.7%, and 25.4% (P=0.001, 0.001, 0.040). There were no differences between external drainage group and control group (P=0.050, 0.070, 0.080); While the values of external drainage group were significantly higher than those in OJ group (all P=0.001). The level of plasma endotoxin was up to (1.49±0.27) EU/ml in OJ group compared with control group 〔（0.27±0.09） EU/ml〕, P=0.001. In external drainage group, the value was （0.91±0.25） EU/ml, which was obviously higher than that in control group and lower than that in OJ group （all P=0.001）. Immunohistochemical study showed b positive expression of ZO-1 dropped from 7/10 in the control group to 6/20 in OJ group （P=0.040）, occludin expression was 8/10 in control group and 7/20 in OJ Group （P=0.020）; expressions of them in external drainage group 〔8/20 （P=0.100,0.210） and 9/20 （P=0.060, 0.200）〕 displayed no significant differences compared with the other twogroups. Quantitative testing of Western blot showed the expressions of ZO-1 and occludin in OJ group were significantly lower than those in control group (P=0.001, 0.010), the values in external drainage group were higher than those in OJ group （P=0.005, 0.014）. The expression of ZO-1 was lower in external drainage group than that in control group (P=0.001), and there was no significant difference of occludin between the two groups (P=0.062）. Conclusion Lack of intestinal bile will undermine the intestinal tight junction protein composition, and make intestinal mucosal barrier impaired. The intestinal barrier more severely injured when biliary tract obstructs because of multiple factors. Bile plays an important role in the maintenance of intestinal mucosal barrier.