Two hundred sixteen previously molted Dekalb Delta Leghorn laying hens (78 wk of age) were utilized to determine the effect of phytase on the ileal digestibility of amino acids. The hens were randomly arranged in a 3 x 2 factorial to evaluate three diet types that were corn-soybean meal (C-SBM), C-SBM-meat and bone meal (C-SBM-MBM), and C-SBM-wheat middlings (C-SBM-WM) and two levels of phytase (0 or 300 U/kg of diet). Each treatment was administered to four replicates of nine hens per replicate. Hens were fed the experimental diets for 21 d, and daily egg production and feed intake were recorded. After 21 d, the hens were euthanized, and ileal contents were collected for amino acid and digestible energy determination. Egg production of the hens did not differ among the treatments (P > 0.05). A significant interaction between diet type and phytase level for Ala, Gly, Leu, and Met was observed. The interaction resulted because phytase numerically increased amino acid digestibilities for the C-SBM-MBM and C-SBM-WM diets, but phytase addition numerically decreased the amino acid digestibilities for the C-SBM diet. Diet type had a significant effect on digesibilites of most amino acids. The latter effect was due primarily to lower amino acid digestibilities for the C-SBM-MBM diet than the C-SBM-WM diet. Phytase had no significant affect on digestibility of any amino acid. Ieal digestible energy was significantly affected by diet type but not by phytase. In conclusion, diet type had a significant effect on apparent ileal amino acid digestibility and digestible energy, but phytase had no consistent effect.