There are several factors related to dietary Ca that may influence digestibility of amino acids (AA). By chelating to dietary phytate, dietary Ca can form non-digestible Ca-phytate complexes, and this may result in reductions of P and AA digestibility. However, adding Ca to diets may increase activation of proteases as co-factors, which could result in increased AA digestibility. In contrast, pH in the digesta may be increased by adding Ca to diets, which likely will have a negative effect on activation of protein digesting enzymes. However, to our knowledge, no data demonstrating effects of increasing dietary Ca on digestibility of AA in pigs have been reported. Therefore, the objective of this experiment was to test the hypothesis that the concentration of Ca in diets affects apparent ileal digestibility (AID) of AA by pigs.