An experiment was conducted to investigate the effect of some herbal plant's powder; garlic (Allium sativum), thyme (Thyme vulgaris) and their mixture in broiler diets on growth performance, carcass traits, some blood components and economical efficiency. A total of 210 unsexed Arbor- Acers 1 day old broiler chicks were randomly distributed into 7 comparable groups, 30 chicks each. Each group was fed one of seven diets during the experimental period (from 1 to 35 days of age). Diet 1, control (with no garlic or thyme powder supplementation) while diets from 2 – 7 contained garlic or thyme as follows: diet 2: control diet + 1% garlic; diet 3: control diet + 2 % garlic; diet 4: control diet + 0.2 % thyme; diet 5: control diet + 0.4 % thyme; diet 6 : control diet + 1 % garlic + 0.2 % thyme;  diet 7: control diet + 2 % garlic + 0.4 % thyme. Results revealed that increasing dietary garlic or thyme significantly (P ≤ 0.05) improved body weight (BW), body weight gain (BWG), performance index (PI) and feed conversion (feed/ gain). While, feed intake was significantly (p ≤ 0.05) decreased with increasing dietary garlic or thyme. Also, water consumption and some blood serum components were significantly affected by the addition of garlic or thyme. Dressing percentage was not affected, while, lymphoid organs weight were significantly increased with increasing dietary garlic or thyme.  Findings of this study indicate that broilers consuming control diet can achieve maximum performance and economic efficiency when supplemented with 0.4% thyme (group 5) without any side effects.