Four essential oils (oregano, thyme, peppermint and garlic) were in vitroevaluated for their antimicrobial activity against some pathogenic microorganismwith concentrations of 10, 20, 50, 75, and 150μg/ml. The laboratoryresults showed that oregano and garlic essential oils were found to be more effective against all tested pathogenic microorganism.Consequently, the oregano essential oil and garlic powderwere chosen as feed additives on diets of quail birds. A total number of 480 Japanese quail chicks, 10 day old, were randomly selected, weighed and divided into eight experimental groups each of 60 birds (3 replicates each of 20 birds). The first group was fed on basal grower diet (considered as control). The second group was fed on diet supplemented with 1.0g oxytetracycline /kg diet. Birds of the 3rd, 4th and 5thgroups were fed on diets supplemented with oregano essential oil at levels of 50, 100 and 150 mg/kg combined with 0.5g oxytetracycline /kg diet, respectively, while birds of the 6th, 7th and 8th groups were fed on diets supplemented with garlic powder at levels of 0.1, 0.2 and 0.3 g/kg combined with 0.5g/kg oxytetracycline, respectively. The obtained results showed thatchicks fed on the dietsupplemented with 150 mg/kg oregano combined with 0.5g/kgoxytetracycline significantly improved body weight, body weight gain, feed conversion, carcass weight and economic efficiency.Moreover, it had the lowest intestine pathogenic populationscontent andmortality percentage followed by those fed on the diet supplementedwith 0.2 g/kg garlic powder combined with 0.5g/kg oxytetracycline.