The aim of this study was to elucidate the pathogenesis of ascending cholangitis after biliary reconstruction, with special reference to the causative role of the defunctionalized jejunum, which is used for anastomosis with the biliary tract. Thirty adult dogs were divided into the following five groups according to the mode of biliary reconstruction : Roux-Y cholecystojejunostomy using a 5-cm (RY-5 cm group) or a 30-cm (RY-30 cm group) jejunal limb and cholecystoduodenal interposition using an iso-peristaltic 5-cm (1-5 cm group) or a 30-cm (1-30 cm group) jejunal limb or a anti-peristaltic 30-cm jejunal limb (RI-30 cm group). In these models, reflux of a meal into the liver was likely to be provoked in those with a short jejunal limb such as the RY-5 cm and I-5 cm groups, while stagnation of bile in the limb was likely to be provoked in those with a long limb, especially the RI-30cm group. In all five groups, the fractions of bile acids and bacterial flora in the jejunal limbs were investigated before and at four weeks after reconstruction. In addition, the function and histology of the liver were examined. Unconjugated bile acids in the jejunal limbs of the RI-30 cm and I-30 cm groups showed a tendency to increase, which was associated with marked bacterial overgrowth. Histologically, ascending cholangitis was confirmed in all of the groups, with the RI-30 cm group showing the most severe inflammation, such as microabscess formation in addition to leukocyte infiltration of the glissonian sheath and the sinusoid. Significant elevations of serum bilirubin, GOT, sialic acid and γ-GTP were seen only in the RI-30 cm group. We conclude that ascending cholangitis after biliary reconstruction is caused by bile stasis and bacterial overgrowth in the jejunal limb, rather than by reflux of a meal. Therefore, biliary reconstruction using a jejunal limb of short length and good motility is recommended in order to prevent ascending cholangitis.