A Factorial experiment (2 × 2) was designed to investigate the effect of dietary phytobiotics (onion and thyme powder) and their interaction on growth, feed utilization, serum biochemical and chemical composition of whole Nile tilapia. Four experimental diets were fourmulated; Diet 1 without addition, Diet 2 containing 5.0 g kg^-1 onion powder, Diet 3 containing 5.0 g kg^-1 thyme powder, Diet 4 containing 5 g onion powder + 5 g thyme powder kg^-1 diet. Each treatment group was assigned randomly in duplicate groups of 25 fish (4.51 ± 0.01 g/fish) in 8 plastic tanks for 84 days. The highest values of FBW, WG and SGR (%), PPV, FR and ER were recorded in Diet 4 but, the highest value of PER was obtained by fish fed diet Diet 2 supplemented with 5 g kg^-1 diet onion. The best value of FCR was obtained in groups Diet 4. ALT and AST activites were significantly decresed by addition of onion and thyme powder (5 g kg^-1 diet). Whereas, the lowest total protein, globulin and albumin values were estimated by fish fed on Diet 1. Supplementation of onion and thyme powder (5 g kg^-1 diet) in the diets of Nile tilapia significantly effected on CP of whole – body of tilapia.