Although exogenous protease enzymes have been used in poultry quite extensively, this has not been the case in pigs. In general, due to their better fermentative capacity and longer digesta transit time in the gut, pigs have greater capacity to digest nutrients than poultry. In young pigs however, the digestion of nutrients, particularly of dietary proteins is marginally incomplete. Therefore, a study was conducted to elucidate the effects of a commercial protease enzyme supplemented in weanling pig diets. The indices of growth, nutrient digestibility, blood profiles, fecal microflora, fecal gas emission and fecal scores were measured during the study. A total of 50 weanling pigs (6.42 ± 0.60 kg) at 28 d of age were randomly assigned to receive 1 of 2 dietary treatments: (1) basal diet (corn-soy based) with no supplemental protease, and (2) basal diet + 200 g/ton protease for 42 d. A completely randomized block design consisting of 5 replicate pens per treatment with 5 pigs per pen was used. Growth performance in terms of bodyweight and average daily gain in pigs fed with protease enzyme (27.04 vs. 25.75 ± 0.25 kg and 491 vs. 460 ± 6 g; P < 0.05) was increased significantly, but gain per feed was similar between treatments. Compared with the control, protease supplementation increased (P < 0.05) the apparent total-tract nutrient digestibility (84.66 vs. 81.21 ± 0.91 DM and 84.02 vs. 80.47 ± 0.95 N) and decreased (P < 0.05) the NH₃ emission (2.0 vs. 1.2 ± 0.14 ppm) in the feces. Except for a decreased (P < 0.05) in blood creatinine level, no differences were observed in RBC, WBC, lymphocytes, urea nitrogen, and IgG concentrations between treatments. Fecal score and fecal microflora (Lactobacillus and E. coli) were also similar between the control and the protease-supplemented diets. Overall, the supplementation of protease enzyme in weanling pigs resulted to improved growth rate and nutrient digestibility. Exogenous protease enzyme reduced fecal NH₃ emission, thus, potentially serving as a tool in lowering noxious gas contribution of livestock production in the environment.