Three hundred of one day old Japanese quail chicks were housed in battery cages and kept under similar environmental and managerial conditions. During raising period the temperature was set initially at 37 ºC and gradually reduced at a rate of 3 ºC/week until 28^th days old was reached. At that time, birds were randomly distributed into five groups (60 chicks each) with four replicates (15 chicks each) to examine the effect of heat stress on performance, behaviour, carcass traits and some blood constituents. The five groups were reared for 15 days (5^th and 6^th week) at 22, 29, 34, 36 and 40 ºC respectively. Diet was formulated to contain approximately 24 % CP and 2.8 Mcal ME/Kg as recommended by NRC, (1994). The birds were fed ad-libitum on the mash diet and given free access to fresh and clean water. The results indicated that, there was a linear decrease in body weight gain, feed intake and feed conversion with increased environmental temperature. Heat stress significantly (p < 0.05) affect the ingestive, social, locomotor and non aggressive pecking behaviour of the experimented quails. Dressing %, liver and gizzard weights were significantly (p < 0.05) decreased, while, heart % was significantly increased with increasing the environmental temperature. The results also indicated that, the estimated blood parameters were affected significantly (p < 0.05) by heat stress. It could be concluded that, heat stress affects the quail performance and the optimum obtained at 22 ºC.