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Abstract This experiment was designed to the study of Phytase Supplementation on egg production and egg shell quality of aged laying hens. The main results could be summarized as follows; This study was carried out at the poultry breeding Farm, Poultry Production Department, Faculty of Agriculture, Ain Shams University. The study aimed to investigate the effect of different levels of phytase on egg production and eggshell quality measurements in laying hen of (Hy-lineW36 and Brown) layers during the last period of production. Feed was offered ad lipitum in metal feeders for each 2hen; water was supplied through automatic nipples. The layers were directly fed a diet according to the producer recommended manual guide of Hy-Line layers 2011 up to 52 week of age to 64 week of age as control treatment and supplied 2 levels of phytase (300FTU-450FTU). Results demonstrated highly significant difference between strains for body weight, whereas the brown strain had significantly heavier body weight compared to the white ones. The present results indicated that no significant difference between strains for egg number. The main effects data indicated that the body weights at 52 week of age weren’t significantly different on brown strain groups, and at the other ages was significantly different in white strain groups, but in all stages ph.2 with other experiment treatments weren’t significantly different (P ˃0.05) compared control. Body weight at 60 and 64 weeks of ages in treatment showed higher body weight of ph.2 group in tow strains more than other treatments, and treatment of ph.1 in the same ages compared with control treatment. The brown layers significantly consumed more feed compared to the white counterparts. Concerning Feed conversion ratio, the present results showed that strain and layers age had highly significant effect on Feed conversion ratio. W-36 layers strain had better feed conversion ratio (1.84) compared to brown layers strain (1.97). Feed conversion ratio increases with advancing of layers age. Consequently, feed efficiency decreases Supplementation of phytase in normal, corn-soybean meal diets improved egg mass. Increase egg mass may be due the increase egg production as egg number/hen, the result reported that, laying hens fed a diet with phytase had significantly higher egg weight than hens fed on the same diet without supplemental phytase (control) showed that in white strain There was no significant difference among treated group’s on egg weight was not significant. Results showed that Phytase supplementation by levels (300 FTU kg-1 of feed) significantly improved all traits, while levels in white strain (450 FTU kg-1 of feed) of phytase supplemented laying hen diet |