This experiment was conducted to determine the efficacy of β-mannanase supplementation to corn SBM based diet on ileal digestibility of nutrients and amino acids in growing pigs. Twenty barrows [(Landrace × Yorkshire) × Duroc] with an average body weight of 25 kg were fasted for 16 h and T-cannulas were surgically attached 15 cm proximal to ileo-cecal junction upon induction of anesthesia. The experimental diet consisted of corn based hulled or de-hulled SBM supplemented with or without 400U β-mannanase/kg. Cannulated pigs were allotted to one of 4 dietary treatments plus a nitrogen-free diet in a completely randomized design with 4 pigs per treatment. A nitrogen-free diet was used to determine basal endogenous losses of CP and amino acids. Data were analyzed as a completely randomized design with 2 × 2 factorial arrangement using GLM procedures of SAS. The main effect included dietary SBM (hulled vs dehulled) and with or without β-mannanase supplementation as well as the interaction between β-mannanase and types of SBM. Each experimental period consisted of 7 d of diet adaptation followed by total feces and ileal digesta collection. The supplementation of β-mannanase improved (P < 0.05) apparent ileal digestibility (AID) of DM compared with non-supplemented in hulled SBM (80.9% vs. 77.2%) and in de-hulled SBM (83% vs. 79.5%) but it did not influence N and GE digestibility. The AID of Thr and Pro was higher (P < 0.05) in dehulled SBM (81.3%, 82.6%) than hulled SBM (77.3%, 78.0%). Likewise, the SID (standardized ileal digestibility) of Thr and Pro was higher (P < 0.05) in dehulled (87.3%, 83.9%) than hulled SBM (83.9%, 80.3%). The supplementation of mannanase led to higher (P < 0.05) AID of amino acids such as Arg (78.2, 79.6% vs. 74.0, 75.5%), His (82.2, 83.2% vs. 79.0, 81.5%), Lys (84.6, 86.9% vs. 79.4, 80.1%), Val (78.2, 80.2% vs. 74.3, 76.7%) and Gly (81.2, 82.9% vs. 77.1, 80.3%) in hulled and dehulled SBM than non-supplemented diet and higher (P < 0.05) SID of Lys (89.0, 89.8% vs. 84.2, 87.0%) in hulled and dehulled SBM than non-supplemented diet. In conclusion the supplementation of enzyme increased the AID of Arg, His, Lys, Val and Gly and SID of Lys.