The present study was conducted to determine the effect of dietary phytase (PHY) levels (500, 1000, 1500 FTU) supplementation to soybean meal (SBM) based diets on feed utilization and the potential replacement of fishmeal (FM) entirely by SBM in Nile tilapia diets. Five isonitrogenous and isocaloric diets containing 28% crude protein and 425 kcal/100 g diets were formulated. The treatments were: (T₁) positive control diet (FM-based), (T₂) negative control diet (SBM-based), (T₃) SBM-based+ 0.50 g PHY/kg, (T₄) SBM-based+ 1.0 g PHY/kg and (T₅) SBM-based+ 1.50 g PHY/kg. Each diet was offered twice daily to apparent satiation in triplicate fish groups (3.12 g/fish) for 11 weeks. The highest significant means (p≤0.05) of growth performance and survival rate values and the best values of feed conversion ratio, protein efficiency ratio, protein productive value %, and energy retention% were achieved by fish fed FM-based diet and SBM-based diet supplemented with 1.0 g PHY/kg compared to the other treatments. Insignificant differences (p>0.05) were found in body composition among treatments groups. Results of this study showed that the addition of phytase as mix to soybean meal-based diets at a rate of 1000 FTU/kg can improve the nutrient utilization and growth performance of Nile tilapia. Also, it has an economic return and reduced the feed cost.