J apanese quail used in poultry industry for its meat and egg production due to many features such as low feed intake, low rearing area requirements, low breeding cost and high disease resistance (Narinc et al., 2010). Based on these advantages, the reared number of quails is gradually increasing in the world poultry industry as a valuable source for eggs and meat production. Commercially, quails are produced mainly for meat production in Europe countries and for egg production in Japan and used as a dual-purpose birds in many Asian countries (Minvielle, 1998). The National Research Council recommendations of crude protein was 24 % for growing Japanese quails (NRC, 1994). Global environment suffering from pollution from ammonia emission and nitrogen excretion from poultry industry, beside that the protein being the most expensive diet component which affect the total cost of production, so the recent trends are decreasing the protein levels in poultry diets without significant effects on production performance. Wen et al. (2017) recorded that quails reared on diets with crude protein range 17.61-25.32 % had no significant influence on carcass yield at 42 days of age. Most breeding programs that aimed to improve meat production are focused on increase live body weight and feed intake at fixed ages, and most studies carried out to increase the body weight in early periods using genetic selection which represent an important tool for genetic improvement in animal breeding program (Hassan, 2011; Fadhil and Hassan, 2018) or using outbreeding mating system between lines to get heterosis in the next generation (Hassan and Ali, 2017). Phenotypic selection used research Article Abstract | Japanese quail is an interested bird due to its early sexual maturity, high egg production and low requirements of housing space and feeding cost. Genetic selection was conducted for high four week body weight in Japanese quails using two different nutritional environments to determine the effect of nutritional environment on selection response of body. Japanese quails were selected under standard crude protein level diet (24.15 % CP) referred as SHW line, and under a low protein diet (18.07 % CP) referred as LHW line, and kept a control line for each nutritional environment as SCL and LCL respectively. The results showed that selection response for body weight of females in low protein diet (27.73 g.) was higher than males and females in selected line in standard protein diet (20.77 and 20.70 g. respectively). In general there were significant heavier body weight of birds in standard crude protein diet compared with low crude protein diet in each of base population, selected parents and progeny in first generation. There were significant differences between SHW and LCL in body weight and weight gain at six weeks of age, while there were significant differences between LHW and both SCL and LCL in feed intake and feed conversion at six weeks of age.