In this study, Nile tilapia was fed experimental diets containing different levels (0, 1, 2, and 3%) of fructooligosaccharide (FOS) for 6 weeks to investigate its effect on the antioxidant activity, non-specific immunity and growth performance of Nile tilapia. Liver and serum samples were taken after 3 and 6 weeks feeding. Results showed that malondialdehyde level and superoxide dismutase activity decreased significantly (P0.05) in other treated groups fed for 6 weeks compared to the control. Weight gain also recorded significant increase in group fed 2% FOS for 6 weeks. These results indicated that dietary FOS supplementation could significantly enhance the antioxidant activities, non-specific immune response and growth performance of Oreochromis niloticus. It could be conclude that 2% dietary FOS was the most suitable and beneficial dose for Nile tilapia.