This study was conducted to evaluate the use of a dietary citric acid as organic acid supplementation on growth performance, feed utilization, hematology and immune response of Nile tilapia, O. niloticus. A total of 720 apparently healthy O. niloticus fingerlings with an averages of body weight and length 5.6 ± 0.14 g and 7.0 ± 0.11 (mean ± SE) were randomly divided into three equal groups (G1, G2 and G3). G1 was fed a basal diet (without citric acid supplementation), while G2 and G3 were fed a dietary citric acid supplementation mixture in 0.5 and1 g/kg diet, respectively in triplicate for 90 days (from 1/8/2017 to 30/10/2017). At the end of  period (90 days), groups G2 and G 3 had significant (P > 0.05) in all the parameters analysed (water quality parameters, growth performance, feed utilization, hematology and immune response of  male Nile tilapia (O. niloticus) fingerlings compared with the control diet group(G1). Blood parameters were significantly (P < 0.05) lower in the control diet than the other experimental diets, which did not significantly differ from each other (P > 0.05). Fish fed diet G3 (supplemented with 1.0 % citric acid / kg diet) showed the higher serum total protein content, while the control group showed the lower serum haematological parameters compared with the other groups (P ≤ 0.05). The average value of (ALT), and (AST) were significant decreased (P< 0.05) compared with control and other diet the addition of citric acid. The present observations suggest that, the growth, feed utilization, and health status of O. niloticus fingerlings can be enhanced with a supplementation with a dietary citric acid as organic acid supplementation improves growth performance, feed utilization, Proximate composition of body muscle, hematology and immune respons of Nile tilapia, O. niloticus fingerlings.