In the past 20 years, broiler production has increased in hot climate countries, due to a greater potential for further growth. Thus, there is a necessity to improve thermotolerance of broilers produced in hot climates. Incubation period will become increasingly important in enhancing thermotolerance, because higher temperatures during incubation may lead to an elevation of the thermoregulatory set-point after hatch. Two recent experiments, conducted to determine the effect of high incubation temperature (INC(HIGH)) from d 10 to 18 on hatching performance and carcass characteristics of broilers, have been compared with broilers from incubated at control temperatures (INC(CONT)). INC(HIGH) resulted in a delay in external pipping and hatching times compared with INC(CONT). There was no incubation temperature effect on the weights of bursa of fabricius, spleen and lungs, and moisture content of chicks but lowered heart and liver weights. When broilers exposed to daily cyclic high temperature from 21 to 42 d, slaughter weight of broilers from INC(CONT) reduced while heavier body weight and breast yield were obtained in broilers from INC(HIGH). It was concluded that higher incubation temperature from d 10 to 18 for 6 h/d had no effect on chick weights and minimized the negative effect of heat stress on slaughter weight and breast meat yield.