Abstract: This experiment was conducted to determine the effect of microbial phytase supplementation accompanied with different levels of dietary calcium on the performance and egg shell quality of laying hens. A factorial design of four levels of calcium (3.8, 3.4, 3.0 and 2.6%) and two levels of microbial phytase (0 and 300 FTU kg-1) was carried out. A total of 72 LOHMAN LSL WHITE laying hens were used. The eight dietary treatments consisted of the corn-SBM basal diet. The metabolizable energy, protein and marginal level of phosphorus were maintained constant in all dietary treatments at 11.56 MJ kg-1, 16.3 and 0.33% TP (0.12% NPP), respectively. Performance and eggshell quality were measured from the age of 22 to 38 weeks. Egg mass, feed efficiency, body weight, eggshell percentage and eggshell density were reduced significantly when hens were fed on 2.6% of dietary calcium level regardless of the presence or absence of phytase. The average eggshell density and shell percentage were significantly increased when hens were fed 3.4% of the Ca level in the presence of phytase. Furthermore, a significant interaction between treatment and age was observed on the eggshell quality. Egg production, egg weight, egg mass, feed intake, feed efficiency and body weight were not affected by phytase enzyme. The information obtained from this experiment indicated that 0.33% TP (0.12% NPP) appears to be sufficient for maintaining production performance and eggshell quality in LOHMAN LSL WHITE laying hens fed the corn-SBM diet containing 3.4% calcium and supplemented with phytase.