Three experiments were conducted to assess the effect of adding a fungal protease to low (LP) and high protein (HP) diets on the apparent ileal digestibility (AID) of amino acids (AA) and performance of growing pigs. In Experiment 1, eight pigs, fitted with two cannulas (proximal duodenum and distal ileum) were used. Twenty eight pigs were used in Experiments 2 and 3 (27.5 and 24.0 kg initial body weights, respectively). Dietary treatments (T) for the three experiments were as follows: T1. LP diet; T2. LP plus 0.5 g protease/kg feed (LP-P); T3. HP diet; T4. HP plus 0.5 g protease/kg feed (HP-P). The diets included sorghum in Experiments 1 and 2, and wheat in Experiment 3. The AID of AA, except for leucine, were higher (P<0.01) in pigs fed the HP diets. The addition of protease to the LP diet increased (P<0.01) the AID of AA, except for lysine. In contrast, addition of protease to the HP diet did not affect (P>0.10) the AID of AA. Intestinal disappearance (ID) of AA was higher (P<0.01) in pigs fed the HP compared to the LP diets. Addition of protease to the LP diet increased (P<0.05) the ID of AA, but was still lower than that of pigs fed the HP diets (P>0.05). Pigs fed the HP sorghum diets had a higher daily gain, feed intake and a better feed/gain ratio (P<0.05) than pigs fed the LP diets; however, there was no effect (P>0.05) of CP level in pigs fed the wheat diets. Addition of protease tended to depress performance of pigs fed the sorghum diets, but did not affect the performance of pigs fed the wheat diets. These results suggest that lysine and threonine intakes, rather than the amino acid digestibility are the factors that limit growth in pigs fed LP-amino acid fortified, sorghum-soyabean meal diets. These data also show no beneficial effect of adding a protease to sorghum- or wheat-based diets on the AID of AA and the performance of growing pigs.