The effects of increasing levels of soluble non-starch polysaccharides (NSP) in extruded dog diets were studied in a 3×2 factorial arrangement of treatments using six dogs per diet. The factors examined were diets of different composition giving varying levels of dietary soluble NSP (11, 16 and 20 g/kg), and the presence or absence of an enzyme containing xylanase, β-glucanase and amylase. The diets varying in soluble NSP content were assigned diets A, B and C, respectively, with enzyme or water being added at feeding to each to comprise the six diets used in the experiment. The feed enzyme mixture was sprayed onto the diet at the time of feeding, at a level of 400 ml/tonne of diet. The trial lasted 13 days with faecal collections occurring on the final 5 days. Measurements taken were; faecal score (1 indicating hard faeces, 5 indicating diarrhoea), coefficient of total tract apparent digestibilities (CTTAD), faecal pH, volatile fatty acids (VFA) and lactate. Significant interactions (P<0.05) were present for dietary soluble NSP content and enzyme for CTTAD of starch, fat, dry matter and gross energy. Diets containing 16 g soluble NSP/kg (diet B) and 20 g soluble NSP/kg (diet C) soluble NSP caused decreases in CTTAD (P<0.05), but presence of the enzyme reversed these effects (P<0.05) such that results were equivalent to those in diet A. The CTTAD of protein was decreased (P<0.001) with increased soluble NSP level but increased (P<0.01) with addition of the enzyme. Increased soluble NSP levels caused faecal deterioration (2.2 versus 2.5 versus 3.0 for diets A, B and C, respectively), however the enzyme decreased faecal score (2.7 versus 2.5, P<0.05). Increased dietary levels of soluble NSP decreased faecal pH (P<0.001) and caused the faecal lactate and VFA concentrations to increase and decrease, respectively (P<0.05), indicating that fermentation in the large intestine was increased. Increasing levels of soluble NSP in dog diets caused some anti-nutritive effects and deteriorated faecal quality, however the addition of the enzyme alleviated some of these effects to the extent that a moderate increase in dietary soluble NSP levels could be tolerated in dog diets based on wheat, barley and mill mix without major detrimental effects on digestion and faecal quality.