A 3x2 factorial experiment was designed to examine the effects of dietary fructooligosaccharides (FOS) level, and the presence or absence of an enzyme (inulinase), on aspects of faecal quality and apparent coefficients of nutrient digestibility in doxs. Three extruded dry diets based on wheat, pearl barley and wheat by-products were formulated to contain (dry matter basis) 1.75g/kg (Diet A), 4.7 g/kg (Diet B) and 61.7 g/kg (Diet C) FOS. The FOS content of Diets B and C was achieved by adding 30 and 60 g/kg (DM) Raftilose®P95, a commercial FOS product. The addition of inulinase (500 ml (1.2x10⁶U) per tonne) was examined for each diet to counteract any potentially negative effects of added FOS on faecal quality and digestibility, and was sprayed onto the diet at feeding at a level of 500 ml per tonne of food. The experiment lasted 13 days with faecal collections occurring on the final 5 days. Measurements taken were: faecal score (one indicating hard faeces, five indicating diarrhoea), coefficients of total tract apparent digestibility (CATTD), faecal pH, and volatile fatty acids (VFA) and lactate concentrations. The CATTD for fat and energy decreased with greater levels of dietary FOS. Increased levels of FOS decreased (P<0.05) faecal pH and the content of dry matter (DM) in the faeces and also increased (P<0.05) the faecal score, although this remained in the 'ideal' range of 1.5-2.5. Addition of inulinase increased (P<0.05) the faecal pH. Faecal lactate concentrations increased with greater levels of FOS (P<0.05; 84.9 versus 142.5 versus 288.7 mmol/kg faeces DM for Diets A, B and C, respectively), suggesting that the growth and (or) activity of lactate-producing bacteria in the colon were enhanced. Higher levels of FOS in an extruded dog food caused faeces to become wetter and more acidic, and consequently the number of dogs that had unacceptable faecal scores increased. However, and at the highest dietary FOS level (61.7 g/kg DM), inulinase caused significantly drier faeces and increased the number of dogs within the 'ideal' range of faecal score.