In order to study the influence of biliary tract obstruction on enteromicroflora,we ligate the canine biliary tract to observe the acrobic and anerobic bacteria in the duodenum and ileum at intervals of post-ligation(the 10th,20th,30th days),and to study the pathogenesis and ultramicroscopic of the ileal mucosa at the same intervals.The results showed that:the population and species of enteroflora in small intestine gradually increased after biliary obstruction.Bacteria(especialy E.coli) ascended to the upper part of small intestine,from their normal habitant of lower part of small intestine.Therefore the radio of general aerobia and E.coli risen obviously in duodenum.The longer the obstruction,the more pathologic changes were observed in ileal mucosa.such as edema,leukocytes infiltration and destruction of epithelial villi.All of those changed may be the causative factor of biliary tract infection.So that,in the programs of preventing enterogenic infection at the state of biliary tract obstruction,the protection and adjusting of normal enteroflora should be adventently considered.