Aquaculture is the last frontier to solve the problem of the global deficiency of white protein. Some studies reported that, nano-particles have enormous potential in controlling the pathogens, improve the immune and growth functions in aquaculture. The present investigation was carried out to evaluate nano-ZnO (nZnO) in comparison to its conventional form as a fish feed additive in growth promoting and immunostimulation of Nile tilapia (Oreochromis niloticus). Zinc oxide nanoparticles were prepared using the chemical method and mixed with the fish feed. 405 Oreochromis niloticus were fed for 120 days on Zinc oxide conventional bulk scale (ZnO) and nanoscale (nZnO) supplemented feed in different concentrations (15, 30, 45 and 60 mg/kg of the feed) in addition to the control which was fed on ZnO free feed. nZnO (15mg/kg) achieved specific growth rates like the higher concentrations of bulk ZnO (60mg/kg). The 60mg/kg nZnO gave the highest rates of Specific growth rates(4 folds than control). growth hormone was higher in serum of fish fed on nZnO supplemented feed than the bulk form. Immunity was assessed through the measurement of total protein and IgM titer and IL1-beta (IL-1β) gene expression. Total protein and IgM titers revealed high values increasing with the increase of concentration of ZnO feed additive in its two forms compared to the control, but nZnO showed better results than conventional ZnO. Analysis of IL1-beta gene expression revealed that 60mg/kg conventional ZnO was the best concentration for up-regulating the IL1-beta followed by the concentration 30mg/kg in the two forms; the nano and the conventional form. The inorganic conventional ZnO up-regulated the IL- 1β better than the nZnO form. Zinc was concentrated higher in muscles of fish fed on nZnO supplemented feed more than conventional ZnO fed fish but still within the permissible limits. One way ANOVA statistical analysis was used in all analyses with p<0.05.