. This study aims to investigation of used Bacillus subtilis and combination between Citric acid and Bacillus subtilis in diets of Nile tilapia (O. niloticus) juveniles and affected on Histopathology and morphometric assessment of intestine, growth, feed utilization and body composition. Nile tilapia were fed control diet (D1) without addition, additive Bacillus subtilis (BS) at a rate 10cm/kg diet (D2), 10cm (BS)+5g citric acid/kg diet (D3) and 10cm (BS)+10g (CA)/kg diet (D4) for 90 days. Results showed that morphometric assessment of intestine improved and significant difference in duodenum, jejunum and ileum in mucosal length and villi length between all treatments except mucosal length in duodenum. Also, these results showed the highest values and best group D4 to contain (10cm BS+10g CA) followed by D3 to contain (10cm BS+5g CA) and the lowest values showed in control group (D1). Also, histopathology of intestine showed that duodenum, jejunum and ileum of fish from group control and D2 showing normal villi and normal mucosal lining. On the other hand, results of intestine of fish from group D3 and D4 showing increase the villi length in duodenum, increase the villi length and branches in jejunum and normal mucosal lining in ileum. Results of body weight gain, SGR, condition factor, FCR, FE, PER, PPV and chemical composition of fish showed improvement and significant differences (P≥ 0.05) between all treatments contain citric acid and Bacillus subtilis compared to control