Abstract: In this study, the citric acid and microbial phytase combination effect on the egg quality characteristics in commercial laying hens of Hy-line (W-36) strain in 53-64 week of age is studied. One hundred and ninety two of laying hens were tested. The experimental design was completely randomized design with a 3H2 factorial arrangement with three levels (0, 2 and 4%) of citric acid and two levels (0.0 and 300 FTU kg-1) of microbial phytase in low available phosphorus diets with 6 treatments, 4 replicates and 8 hens in each replicate. The measurements were specific gravity, eggshell thickness, Hough unit, eggshell weight and eggshell ash. The results showed that interaction of citric acid and phytase had significant (p<0.05) effect on specific gravity, eggshell thickness and eggshell weight. Adding of 4% citric acid to low available phosphorus diets decreased the Hough unit and eggshell ash in comparison with other groups, significantly (p<0.05). 300 unit kg-1 phytase addition in low available phosphorus diets, decreased the Hough unit, significantly (p<0.05). Also, phytase addition in low available phosphorus diets, was increased eggshell ash, significantly (p<0.05).