This experiment was aimed to investigate the effect of phytase, citric acid and their interaction on growth performance, feed utilization, body composition, economic evaluation and its antibacterial activity against fish pathogens of Nile tilapia fingerlings. Nine isonitrogenous 30 % CP and isocaloric 450.26Kcal/100g experimental diets were prepared. Phytase was added at the level 0, 1000 and 2000 FTU/kg diet while citric acid was added at the level of 0, 30 and 60 g in the experimental diets. Six hundred and seventy five of Nile tilapia fingerlings were placed randomly in twenty seven V-shaped fiber tanks 120 L capacity of water /tank, in three replicates per treatment was used in this study. Each tank stocked with twenty five fingerlings of with an average initial body weight of 12.47±0.3g /fish. Fish were acclimated to laboratory conditions for 2 weeks prior before the experimental started. Photoperiod was 12h light/ 12h dark regulate. Fish were hand-fed to satiation, two times daily for six days a week through the whole experimental period (60 days). The results indicated that the best growth performance and feed utilization of Nile tilapia fingerlings fed on D5 (1000 FTU phytase / kg + 30g citric acid/ kg) and the lowest group fed on control diet (D1). While, antibacterial activity showed that citric acid alone and citric acid with phytase had highest activity and gave wide inhibition zones against all tested and isolated bacteria which infect Nile tilapia compare with different used antibiotics. Phytase and citric acid positively affected the growth performance, feed utilization, whole body composition and antibacterial activity against in Nile tilapia (O.niloticus) fingerlings. Moreover, both the supplements interacted significantly with each other for these parameters and that the fish fed on diet No. 5, containing 1000 FTU phytase / Kg with 30 g citric acid/ kg, gave the best results.