A total number of 225 unsexed-one-day old Starbro broiler chicks were randomly distributed into 5 equal experimental groups with three replicates of 15 chicks each. The first group was fed the basal diet and served as control group. The second and third groups were fed the basal diet supplemented with 0.25 and 0.50g Robadiar/kg diet, respectively. The fourth and fifth groups were fed the basal diet supplemented with 0.30 and 0.60g Orego-Stim/kg diet, respectively. The effect of these feed additives on performance of broilers were evaluated. The results obtained could be summarized as follows: broiler chicks of the fifth group recorded the best values for live body weight, body weight gain and feed conversion ratio followed by fourth, third and second treatment groups compared with the control diet. Relative weight of eviscerated carcass, heart and edible organs were significantly (P≤0.05) increased by dietary oregano groups (except the second group) compared with the control group. Also, relative weights of thymus and bursa significantly (P≤0.05) increased for the fifth group compared to the control one, while, abdominal fat (%) was significantly (P≤0.05) reduced by dietary treatments. All dietary additives significantly reduced the total counts of anaerobic and E. coli bacteria, at the same time, they increased the beneficial bacteria counts (lactobacillus), moreover, birds of fifth group recorded the lowest counts of both anaerobic and E. coli bacteria, and the highest count of lactobacillus compared to other treatment groups and untreated control group. Chicks fed the fifth diet significantly (P≤0.05) had high plasma total protein, globulin and glucose concentrations compared to control diet. Each of plasma total lipids, total cholesterol and triglycerides concentration was significantly (P≤0.05)decreased in all supplemented diet groups comparing to the control group. However, plasma concentrations of aspartate amino transaminase and alanine transaminase activities as well as albumin/globulin ratio were not significantly affected. There were significant (P≤0.05) increases in the counts of erythrocytes and total counts of leukocytic, but no in  lymphocytes, heterophil and heterophil/lymphocytes ratio due to tested supplements compared to the control. Economic efficiency values increased by about 7.43, 10.00, 15.14 and 16.71% for second, third, fourth and fifth groups, respectively over the control group. Supplementing diet with 0.60g Orego-Stim/kg diet significantly improved the growth performance, carcass characteristic and some physiological and immunological parameters of broiler chicks.