A total of 140 growing pigs [Duroc × (Yorkshire × Landrace)] with an average body weight of 24.10 ± 1.66 kg were used in a 6 wk trial to determine the effect of dietary protease supplementation to low- and high-energy diets for pigs. Pigs were randomly allowed to one of four dietary treatments in a 2 × 2 factorial design with two levels of energy and 0 or 125 g ton^-1 of protease. During 6 wk, pigs fed on the high-energy diets had greater (P < 0.05) average daily gain (ADG), gain to feed ratio (G:F), and energy digestibility than those fed low-energy diets. Protease supplementation increased (P < 0.05) energy digestibility and creatinine levels in the blood. Also, protease supplementation tended to increase (P < 0.1) dry matter digestibility, G:F, blood urea nitrogen concentrations and to decrease (P < 0.1) ammonia gas emission, and norepinephrine levels in the blood. In conclusion, dietary supplementation with 125 g ton^-1 protease has beneficial effect on growth performance and nutrient digestibility. The noxious gas emission was also reduced in pigs fed protease-supplemented diets. In addition, ADG and feed efficiency were improved in pigs fed high-energy diets.