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 erythrocyNAC, Vit. C and vit. E combination treated birds of NHST and HST groups (group IV, V and VI) exhibited significantly increased activities of erythrocyte CAT, GPX and GSH levels, while MDA level showed significant decrease when compared with HST-untreated Plasma activities of SOD at 31 & 43 days and CAT at 31 days were significantly decreased, while MDA level at 21 & 31 days showed a significant increase in HST groups (II & III) when compared with group I (Table 5.a and 6.a). It was also observed that NAC,HST-untreated birds of group II and group III showed significant decrease in the activities of liver SOD, CAT and GR in addition to GSH, vit. C and vit. E concentrations while GPX activity and MDA level showed a significant increase when compared with groSimilarly, the activities of liver SOD, CAT, GPX and GR, in addition to GSH, vit. C and vit. E levels showed significant increase, while MDA level showed significant decrease which be noticed in NAC, vit. C and vit. E combination treated birds of group IVThere were significantly down regulation in pattern of expression of Mn-superoxide dismutase and catalase in both one day heat stress and two days heat stress groups. Meanwhile, the levels of gene expression of Mn- superoxide dismutase and catalase were iIt can be concluded from the present study that supplementation of antioxidants (NAC, vit. C, and vit. E) in broiler feed exerts a heat stress ameliorating effect through alteration in both enzymatic and non-enzymatic antioxidative systems of erythrocytes