The experimental work of the present study was carriedout at the Poultry Research Station, Poultry ProductionDepartment, Faculty of Agriculture, Fayoum University.Chemical analyses were performed in the laboratories of thesame Department.The experiment was conducted during the period fromMarch to April 2005. The effect of substituting yellow cornby some by-products of medicinal and aromatic plants withor without enzyme supplementation was studied on growingJapanese quail performance. Fourteen dietary treatmentswere designed to study the effects of substituting yellow cornby some by-products of medicinal and aromatic plants withor without enzyme supplementation. The by-products wereparsley, dill and peppermint.Live body weight (LBW) and Live body weight gain(LBWG): Quails fed diet 10 (parsley BP replacing 16% YC+ 0.1% KD) had higher LBW at 38 days of age and LBWGduring the period from 10 to 38 days of age. Quails fed diet13 (peppermint BP replacing 16% YC) had lower LBW at 38days of age and LBWG during the period from 10 to 38 daysof age. Quails fed diet 11 (peppermint BP replacing 8% YC)had heavier LBW at 45 days of age and LBWG during theperiod from 10 to 45 days of age. Quails fed control diet hadlower LBW at 45 days of age and LBWG during the periodfrom 10 to 45 days of age.Feed intake (FI): Quails fed diet 2(control + 0.1%KD) had significantly lower FI during the periods from 10 to38 and 10 to 45 days of age.Feed conversion (FC), Crude protein conversion (CPC) andCaloric conversion ratio (CCR): Quails fed diet 8 (parsley BPreplacing 8% YC + 0.1% KD) had the best FC and CCR values duringthe period from 10 to 38 days of age, quails fed diet 2 (control + 0.1%KD) had the best CPC value during the same period (10 to 38 days ofage). Quails fed diet 2 (control + 0.1% KD) had the best FC, CPC andCCR values during the period from 10 to 45 days of age, followed bythose fed diet 14 (peppermint BP replacing16%YC+0.1% KD) duringthe same period. Quails fed diet 5 (dill BP replacing 16% YC) had theworst FC, CPC and CCR values during the periods from 10 to 38 and10 to 45 days.Performance index (PI): Quails fed diet 8 (parsley BPreplacing 8% YC + 0.1% KD) had significantly higher PIduring period from 10 to 38 days of age. Quails fed diet 2 (control + 0.1% KD) had significantly higher PI value duringthe period from 10 to 45 days of age.Slaughter parameters: Quails fed diet 13 (peppermintBP replacing 16% YC) and 14 (peppermint BP replacing 8%YC+ 0.1% KD) had significantly higher gizzard% and totalgiblets%.Serum constituents: Quails fed diet 10 (parsley BPreplacing 16% YC+ 0.1% KD) had significantly higherserum total protein and globulin.Chemical composition of Japanese quail meat: Thehighest moisture and protein (the lowest fat %) value wasobserved for quails fed diet 13 (peppermint BP replacing 8%YC), while those fed diet 2 (control + 0.1% KD) had thehighest fat % (and consequently the lowest moisture andprotein %).Mortality rate: Mortality was zero% in quails fed diet3 (dill BP replacing 8% YC), 4 (dill BP replacing 8% YC +0.1% KD), 5 (dill BP replacing 16% YC), 8 (parsley BPreplacing 8% YC + 0.1% KD) and 14 (peppermint BPreplacing 8% YC+ 0.1% KD). However quails fed diet 9(parsley BP replacing 16% YC) had the highest mortalityrate being 2.9%. The percentage of mortality was 1.5% inquails fed the other diets.Economical efficiency (EEf): Quails fed diet 9(parsley BP replacing 16% YC) gave the best economicaland relative efficiency then quails fed diet 8 (parsley BPreplacing 8% YC + 0.1% KD), and followed by those feddiet 10 (parsley BP replacing 16% YC+ 0.1% KD) duringthe period from 10 to 38 days of age. It can be concluded thatMAPB can be used instead of YC in Japanese quail feeds ata level to substitute up to 16% of YC. The diet of choice isthat containing parsley followed by peppermint then dill.