This study was conducted to determine whether supplemental phytase affects the activities of trypsin and chymotrypsin in the small intestine and the apparent ileal digestibility (AID) of crude protein (CP) and amino acids (AAs) in pigs fed sorghum-soybean meal (SBM) diets. Twelve pigs (22.3 ± 1.8 kg initial weight) were housed individually in metabolism crates. Dietary treatments were a basal sorghum-SBM diet (182 g/kg CP) with or without supplementation of 500 phytase activity units. Both diets met or exceeded the requirements of the indispensable AA, available P and Ca of growing pigs. At the end of the 17-day study, pigs were euthanized to harvest digesta from stomach, duodenum, jejunum, and ileum and measure their trypsin and chymotrypsin activity. The AID of AA was measured in ileal digesta. Phytase decreased trypsin activity in jejunum, increased trypsin activity in the ileum, and decreased chymotrypsin activity in the ileum. Phytase did not affect the AID of CP and AA. Trypsin and chymotrypsin activities were mostly either unaffected or reduced by phytase, which might be a factor in the lack of improved AID of AA and CP in pigs fed phytase-supplemented sorghum-SBM diets.