The effect of fermentable carbohydrates (sugar beet pulp and fructooligosaccharides) on the faecal bacterial communities of weaning piglets was analysed using 16S rDNA-based approaches. Amplicons of the V6–V8 variable regions of bacterial 16S rDNA were analysed by denaturing gradient gel electrophoresis (DGGE), cloning and sequencing. Differences in piglet faecal bacterial community structure were determined based on the Dice coefficients for pairwise comparison of the DGGE fingerprints and revealed significant changes in the faecal microbiota immediately after weaning. Piglets fed with fermentable carbohydrates showed a higher bacterial diversity and a more rapid stabilisation of the bacterial community compared with that of the animals fed with the control diet. Thirteen dominant DGGE bands were matched with sequences that showed 91–97% similarity to those derived from the Clostridium coccoides group and the Clostridium leptum subgroup. Amplicons related to Ruminococcus-like species were found in all DGGE fingerprints derived from pigs on the diet containing sugar beet pulp and fructooligosaccharides, but not in pigs on the control diet. These results indicate that these bacteria may play a role in the utilisation of dietary fibres.