In the experiment accomplished, the effect was studied of fructans and polyphenols, concurrently occurring in a diet, on the functioning of the final section of alimentary tract in experimental rats. Three diets were applied: one control diet (K) with 7.5 % of sucrose and two experimental diets containing: 1) 7.9 % of commercial fructooligosacharride preparation (FOS) and 2) 8.3 % of FOS concentrate made from chicory roots that also enriched the diet with 0.05 % of polyphenols (FOS+PP). Young male Wistar rats (8 rats per group) were ad libitum fed for 4 weeks. The individual feed consumption level and body weight gains of rats were determined. In the caecal contents, the following parameters were measured: pH, dry matter, ammonia, Lowry’s protein, volatile fatty acids (VFA), and activity of bacterial enzymes. Also, the caecum with and without contents was weighed. No statistically significant differences were found between the groups as regards the feed consumption level and body weight gains in rats. The consumption level of feed products containing commercial FOS and the FOS+PP preparation made from chicory roots caused the weight of caecum wall and of its contents to significantly increase (P<0.05) compared to the control group. Significantly lower (P < 0.05) pH values and a lower ammonia concentration in the caecal contents were found in the animals fed with experimental diets. The preparations analysed significantly increased the SCFA quota, especially, they significantly increased the content of propanoic acid and butyric acid when converted to 100 g of body weight. In the FOS+PP group, a significant increase in the concentration of VFA was found in the caecal contents (P<0.05 vs FOS and K). The experimental diets beneficially modified the activity of bacterial β-glucosidase and β-glucuronidase.