Phytate in poultry rations containing rice bran (RB) critically reduce poultry performance while increasing N and P excretion. The objective of this study was to determine whether the anti-nutritive problems associated with higher inclusions of rice bran in poultry rations (up to 40%) could be mitigated with mega doses of phytase. Twenty days old male broiler chicks (n=180) in 60 floor pens were fed on 10 dietary combinations of a completely randomized factorial design (2×5). Two dietary rice bran (RB) levels (20 or 40%) and five levels (0, 1000, 2000, 3000 and 4000 FTU/kg diet) of phytase (Natuphos 500) were main factors. Cage-wise daily feed/water intakes and body weights on day 28, 35 and 42 were determined. Weekly and total weight gain and feed conversion ratio were determined. Cr2O3 mixed diets were fed from day 35 to determine illeal digestibility of crude protein, phosphorus (P) and dry matter. On day 42, following a 12-hour fast, two birds from each pen were humanely slaughtered to determine visceral organ weights. Fat free tibia ash contents and latency-to-lie test done on day 28, 35 and 42 were used as bone parameters. Growth performance parameters were not enhanced significantly due to mega doses of phytase. Negative effects like body weight reductions affected latency to lie time increments and further confirmed by insignificancy of tibia ash increments. Phytase significantly improved the crude protein digestibility. The optimum levels of phytase for the best crude protein digestibility with 20% and 40% dietary rice bran were 3000 and 4000 FTU/kg, respectively. Digestibility values of P and dry matter also affected. Supplementation of mega doses of phytase improved illeal crude protein digestibilities but not growth performances and bone status. Mega doses of phytase did not mitigate the adverse effects of 40% rice bran included broiler diets. Manuscript profile