A total number of 180 Nile-tilapia (Oreochromis niloticus) were divided into four equal groups; the first one served as control fed on basal non-treated diet. The second group fed on diet supplemented with 0.5 ml prebiotic βpolo /kg basal fish diet, the third group on diet supplemented with 1 ml prebiotic βpolo/kg basal fish diet, and the fourth group fed on diet supplemented with 1.5 ml prebiotic β polo/kg basal fish diet for 40 days. The result elevated that, the growth performance was significantly higher in all treatments than in the control group and the highest increased was in the group received 1.5 ml prebiotic βpolo /kg basal fish diet. The hematocrit (HC) values, nitroblue-tetrazolium (NBT) and lysozyme activities were increased significantly in all treated groups than the control and the highest increased was in the group received 1.5 ml prebiotic βpolo /kg basal fish diet. The percent level of protection among the three treated groups after challenge infection using Pseudomonas flourescence (Ps. flourescence) (0.5 ml of culture suspension of pathogen containing 107 bacteria ml-1) was higher than control and the highest record was in the group of received 1.5 ml prebiotic βpolo /kg basal fish diet .