Summary:-Heat stress induced disturbances of antioxidant defense system in chicken, so the aim of the present study was performed with objectives to determine the antioxidant status of chickens subjected to heat stress in addition to gene expression changThis study was carried out in summary season (August) on one hundred, apparently healthy, one day-old, unsexed Hubbard chicks were used. They were provided by Omat El-Saudia Poultry Company at Sharkia Province. After through cleaning and disinfection, theThe chicks were divided into 2 main classes:The first class (untreated): This class is subdivided randomly into three main groups as follow:The first group served as a control for other groups (untreated group & NHST) and reared under ambient temperature (30 ± 2 ºC) daily allover the experimental.The second group: served as one day heat stress group at 40 ± 2ºC for 2, 3 and 4 hr at 20, 30 and 40 days consecquency.The third group: served as two days heat stress group at 40 ± 2ºC for 2, 3 and 4 consecutive hours at 20, 30 and 40 days sequence and for 2, 3 and 4 consecutive hours at 21, 31 and 41 days sequence.The second class (treated): This class is subdivided randomly into three main groups as followThe fourth group: represented NHST, reared under similar condition of temperature as group I and received a mixture of NAC, Vit. C and Vit.E daily allover the experimental .The fiveth group: this group exposed to the same conditions of group II and received a mixture of NAC, Vit. C and Vit.E daily allover the experimental .The sixth group: this group exposed to the same conditions of group III and received a mixture of NAC, Vit. C and Vit.E daily allover the experimental.Blood samples were drained from wing veins of birds from each group at 21, 31, 41 and 43 days of the experimental period. The samples were collected on heparinized clean, dry vials with a rubber stopper to and separate plasma were centrifuged at 3000 r.p.The obtained results showed that:-The status of enzymatic and non-enzymatic antioxidants in erythrocytes of broilers are depicted in Table (3a and 4.a). Untreated birds belonging to group II (one day HST) and group III (two days HST) exhibited significantly low activity of blood erythrocyurea-treated rice straw with addition of 5% molasses or the control. Ingeneral the treatment improved feed intake of rice straw.Nutrient digestibility of the diets: the results revealed that digestioncoefficient of DM and NFE didn’t show any significant (P > 0.05)difference in sheep fed diet contained 4% urea-treated rice straw, whiledigestibility coefficient for DM and NFE in those fed diet contained4% urea-treated rice straw with addition of 5% molasses wassignificantly (P < 0.05) higher as compared to that of the control diet.Ether extract digestibility of the diets contained either 4% urea-treated163