Effects of varying dietary protein and vitamin C levels on several nutritional parameters were calculated for young Oreochromis niloticus. Live body weight of Nile tilapia (O. niloticus) in- creased significantly (P<0.001) with increasing dietary protein level or vitamin C; supplementation in fish diet. Average daily gain weight in- creased with 37.31% in fish fed the high protein diet (31.1% crude protein) than those fed the nor- mal protein diet (25.4%). Also, average daily weight gain increased with 5.41 and 14.86%, respectively, in fish fed diets supplemented with 50 and 100 mg vitamin C/ kg diet than those fed diets without supplementation. Increasing dietary protein level improved the feed conversion. Feed conversion improved by 18.85% in fish group fed High protein diet when compared with those fed the normal protein diet. Feed conversion im- proved by 1.37 and 7.88%, respectively, in fish groups fed diets supplemented with 50 and 100 mg vitamin C when compared with those fed diet without vitamin C supplementation. Serum total protein, albumin, creatinine and AST significantly (P<0.01) increased with dietary protein level, while ALT insignificantly affected. Also, vitamin C supplementation in fish diets significantly in- creased the concentrations of serum total protein, albumin and AST, while the concentration of ALT insignificantly decreased. Fish body composition did not affected significantly with dietary protein level or dietary vitamin C supplementation. The interaction between dietary protein lev- el and vitamin C supplementation did not show any significant differences in body weight, daily gain, daily feed intake, feed conversion, blood components or body composition.