A total number of 400 Japanese quail (Coturnix coturnix japanica) chicks at hatch.The quail chicks were housed in cages at hatch up to 42 days of age. The experiment aimed to study comparative effect of some feed additives as growth promoters suuch as Black seeds cumin (Nigella sativa), Margoram leaves meal (Origanum majorana) (medicinal plants feed additives) or Enzyme preparation (Optizyme) on performance of growing Japanese quail. Quail chicks were divided randomly into 4 equal experimental groups of 100 chicks in four replicates (25 chicks / replicate). The first group was fed the basal diet as a control, while three dietary groups were obtained by adding the tested growth promoters to the control diet. Each one of growth promoters was added to the control diet.EitherasBlack cumin seed or Margoram leaves meal and enzyme preparation (Optizyme) were added to the control diet at an inclusion rate of 1.0, 0.5 or 0.5 g/kg, respectively. The experimental diets were isocaloric (2900 kcal ME/kg), isonitrogenous (24% CP) and isofibrous. Results obtained could be summarized as follows Live body weight and body weight gain of quail chicks were significantly (P<0.05) increased with dietary feed additives. The highest live body weight and body weight gain were recorded by using Black seeds (Nigella sativa) cumin and followed by Margoram leaves (Origanum majorana) meal as feed additives (medicinal plants), while those fed the control diet recorded the lowest values. Feeding quail either black seeds cumin, Margoram leaves meal and enzyme preparation resulted in 10.22, 5.23 and 3.27% higher in live body weight than that of the control group, respectively. It is worthy noting that feed intake significantly (P<0.05) increased among groups, compared to the control diet. Black seeds cumin recorded the best values (P<0.05) of feed conversion ratio (g feed/g gain), while the control diet recorded the worst feed conversion ratio. Mortality rate recorded a non-significant difference between groups. Black seeds cumin recorded the lowest values, while the control group recorded the highest ones. Dressing percentage showed significant (P<0.05) increase with the feed additives. Black seeds cumin recorded the highest values, while edible giblets (liver, heart and gizzard) percentage were insignificantly increased affected by feed additives Digestibility coefficients of OM, CP, CF, EE, NFE and the nutritive values expressed as DCP, TDN % and ME (kcal/kg) were significantly varied (P<0.05) among the different experimental groups. Black seeds cumin group showed the best net return as well as the highest value of economic efficiency among experimental groups. From the nutritional and economical efficiency stand points of view, it could be concluded that, using dietary medicinal plants such as Black seeds cumin (Nigella sativa) at 1.0 g/k of the diet could improve growth performance and economical efficiency of growing Japanese quail.