Polydextrose is a potential prebiotic, but has not been well tested in dogs. Thus, the objective of the present study was to determine the effects of polydextrose on faecal characteristics, microbial populations and fermentative end products in healthy adult dogs. A total of eight adult hound dogs (3·5 (sem 0·5) years; 20 (sem 0·5) kg) were randomly allotted to one of four test diets containing the following concentrations of polydextrose: (1) 0 % (control); (2) 0·5 %; (3) 1·0 %; or (4) 1·5 %. A Latin square design was used, with each treatment period lasting 14 d (days 0–10 adaptation; days 11–14 fresh and total faecal collection). All dogs were fed to maintain body weight. Data were evaluated for linear and quadratic effects using SAS software. Although apparent total tract DM digestibility was unaffected, total tract crude protein digestibility tended to decrease (P < 0·10) linearly with increasing dietary polydextrose concentrations. Fresh faecal DM percentage tended to decrease (P < 0·10) linearly, while faecal scores increased (P < 0·05; looser stools) with increasing dietary concentrations of polydextrose. Faecal acetate, propionate and total SCFA concentrations increased (P < 0·05) linearly with increased dietary polydextrose. Faecal pH decreased (P < 0·05) linearly with increasing polydextrose. Faecal indole tended to decrease (P < 0·10) linearly with increasing polydextrose, but other faecal protein catabolites were not changed. Faecal Clostridium perfringens linearly decreased (P < 0·05) with increasing dietary polydextrose concentrations, but Escherichia coli, Lactobacillus spp. and Bifidobacterium spp. were not affected. Based on the present results, polydextrose appears to act as a highly fermentable fibre, but requires further research to test its potential as a prebiotic in dogs.