A 12-week growth  study was carried out to investigate the effects of water salinity (10 and 15 ppt) and dietary sodium chloride, NaCl supplementation (0, 3 and 6% NaCl) levels on growth performance, survival rate and blood components of juvenile of Nile tilapia,Oreochromis niloticus. The results indicated that final live body weight, daily growth rate, relative growth and specific growth significantly (P<0.001) affected with water salinity, also feed conversion was significantly (P<0.001) improved. Final live body weight and growth rate increased in fish group reared at low water salinity level when compared with fish group reared at the high water salinity. Serum total protein, albumin, globulin, aspartate amino transferase (AST), alanine amino transaminase (ALT), glucose and total lipids concentration insignificantly affected with water salinity. Uric acid and serum creatinine concentration significantly (P<0.001) affected with water salinity. Red blood cells and white blood cells counts increased significantly (P<0.001) with increasing salinity level in pond water, while lymphocytes, monocytes and neutrophil cells insignificantly affected with water salinity. Live body weight, daily weight gain, relative growth rate and specific growth rate, significantly (P<0.001) affected with NaCl supplementation. Fish group fed diets supplemented with 3% NaCl recorded final body and daily gain higher by 11.18 and 25.58% when compared with those fed diet without supplementation, while fish fed diets supplemented with 6% NaCl recorded 4.95 and 18.6%, respectively. Fish group fed diets supplemented with 3% NaCl recorded the best survival rate. Daily feed intake affected significantly (P<0.001) with NaCl supplementation, while feed conversion ratio insignificantly affected with NaCl supplementation. Fish group fed diet supplemented with 3% NaCl recorded higher glucose concentration than the other experimental groups, while this group recorded lower plasma creatinine and uric acid. The obtained results indicated that salinity is a key factor in controlling growth of Nile tilapia.