The present study was conducted to determine the optimum of energy to protein ratio on live performance and carcass characteristics of Japanese quails from 0 to 21d (starter) and from 21 to 45d (finisher) of age. Two hundred and fifty-two Japanese quails (1-day-old) were used in this experiment. A completely randomized design was used. The quails fed with one level of metabolizable energy (ME) 2900 kcal/kg, and three levels of crude protein (CP) include 21, 24 and 27%. Diets fed to birds from 0 to 45d of age. Day-old Japanese quails were assigned into 36 separate floor pens (40 cm 40 cm) with 7 birds per pen and there were 4 replicates under each diet. Body weight gain, Feed conversion ratio (FCR), protein efficiency ratio (PER), mortality and feed cost were recorded in each period at starter, finisher and whole rearing periods. There are not significant differences in the Body weight gain (P > 0.05) of quails in the starter period, but Significant differences were found (P < 0.05) in the finisher and whole rearing periods. The birds fed with diets containing high crude protein (with low ME:CP ratio) had better feed conversion ratio than those fed with other diets. Birds fed ME:CP ratio in the diet had increased mortality in whole period compared to the other periods. Therefore the result of this experiment suggested that it can be using the diets with 107 ME:CP (for starter diets) and 120 ME:CP (for finisher diets) in Japanese quail to obtain the best performance and carcass characteristics.