Abstract: Feeding trials were conducted in glass tanks to assess the effect of toasting and incubation of soybean meal supplemented with phytase (Ronozyme P (5000) CT, Batch HB 955001) in practical diets on the growth, digestibility and mineral deposition in Nile tilapia, Oreochromis niloticus. The diets contained six levels of the enzyme at 0, 2000 units, 4000 units, 6000 units, 8000 units and 10,000 units/kg diet making diet /treatments (1-6). The zero level served as the control. The diets were fed to fingerlings of Nile tilapia (6.23?0.1) at 5% of their body weight, twice daily, for 63 days. At the end of the experiment, fish carcass (whole body) and the faecal matters were analyzed for mineral composition. Results showed no significant differences in the growth and nutrient utilization of the fish fed all the diets. All the fish fed diets that contained phytase had better (P>0.05) growth and nutrient utilization indices than the fish fed diet without phytase. Similarly, the apparent digestibility coefficient (ADC) for protein and gross energy (GE) of fish fed diets with phytase were higher (P> 0.05) than the ADC for protein and ADC for GE of the fish fed diet without phytase. The fish fed diet with 8000 units of phytase/ kg diet had the best mean weight gain, specific growth rate, food conversion ratio, ADC for protein, lipid and GE compared with the fish fed every other diet. The mineral composition (Ca, Mg, P, Fe, Zn, Mn) in all the fish fed the different diets were similar (P>0.05),.though some of the group of fish fed diets that contained phytase had marginally higher mineral concentration than in the fish fed diet without phytase. Faecal P decreased significantly in the fish fed diets with 8000 and 10000 units of phytase/kg diet.