This study was conducted to evaluate the effect of adding Zimoferment on growth performance and immune status of Nile tilapia (O. niloticus). One hundred sixty eight Nile tilapia (0. niloticus) with an average body weight of 40+1.02 g were divided in 4 treatments x 3 replIcations, 42 fish/group, 14 fish in 12 experimental glass aquaria for 60 days. Four isonitrogenous and isocaloric diets containing 35% crude protein and 2.7 kcal/g of metabolizable energy were formulated in which Zimoferment was added, 0%, 1%, 1.5% and 2%, Feed consumption and body weight were recorded biweekly during the experimental period. At the end of the experiment blood samples were collected from all fish to determine the immune status. Results demonstrated that Zimoferment has good potential as Zimoferment up to 1.5% in The highest growth performance and the best feed efficiency were observed with fish fed diets containing 1% and 1.5% Zimoferment. The lowest feed efficiency and growth performance were shown in the fish fed on diets containing 0% and 2% Zimoferment. The phagocytic assay was performed and indicated that the increase of both percentage of phagocytosis and phagocytic index in the group fed on 1.5% Zimoferment compared with the other groups The challenge of the experimental groups was performed using a pathogenic strain of Pseudomonas florescences, via intra peritoneal route, 10 O. niloticus from each group were injected separately by 0.2ml of 24hr broth culture containing Fish clinical abnormalities and mortalities were recorded 106 CFU/ml Pseudomonas florescences. growth performance and immune status of fish. ed and reisolation of the Pseudomonas florescene