The objectives of this study, effects of prebiotic β polo on innate immunity of Oreochromis niloticus (O.niloticus) and increase resist against disease. A total number of 180 Nile-tilapia fish (O. niloticus), were divided into four equal groups; the first one was served as control fed on basal non-treated diet. The second group fed on diet supplemented with 1.5 ml prebiotic βpolo /kg basal fish diet, the third group fed on diet supplemented with 1 ml prebiotic βpolo/kg basal fish diet, and the fourth group fed on diet supplemented with 0.5 ml prebiotic βpolo/kg basal fish diet for 40 days. The results showed that, significant increase in phagocytic activity test and total leucocyte count (TLC) levels. The percent level of protection among the three treated groups after challenge infection using Aeromonus sobria Aer. sobria (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 received 1.5 ml prebiotic βpolo /kg basal fish diet. The results of the present study support the use of 1.5 ml prebiotic βpolo /kg basal fish diet as fish immunostimulants.