The major target of this study was to investigate the physiological changes in broiler chicks during exposure to high ambient temperature and elucidate the protective role of grape seed extract in alleviating these expected changes. One hundred and eighty Hubbard broiler chicks (1d-old) were used in the present work. The brooding temperature was maintained at 34°C (55% RH) for the first 2 days, and then decreased gradually to 24°C (55% RH) until 21 days of age. At day 22, birds were randomly divided into 4 groups with 3 replicates (n=15 in each replicate). Birds in group1 (TN) kept at 24 ± 1C and 55±5% RH and fed on commercial diet as a negative control. Birds in groups 2, 3 and 4 subjected to cyclic heat stress by exposing them to 36±1C and 65±5%RH for 8h (from 10 am to 6 pm) during the period between 22d to 40d of age. Birds in group 2 (HSGSE0) fed on commercial diet without grape seed extract supplementation as a positive control. Birds in groups 3 (HSGSE1) and 4 (HSGSE2) fed on commercial diets supplemented with 100 and 200mg/kg grape seed extract, respectively. Results showed that heat stress significantly increased body temperature (BT), respiratory rate (RR), heterophil/lymphocyte (H/L) ratio, corticosterone (CTC), triglycerides (TG), low density lipoprotein (LDL), high density lipoprotein (HDL) and liver malondialdehyde (MDA) and decreased liver superoxide dismutase (SOD) and glutathione (GSH) compared to TN group. Although BT and RR were not affected by GSE supplementation ( 100 or 200mg/kg GSE), liver SOD and GSH were significantly increased and H:L ratio, CTC, TG, LDL, HDL and liver MDA were significantly decreased by GSE supplementation compared to GSE0 group. In conclusion, the obtained data demonstrate that grape seed extract could relieved some negative effects (stress indicators, lipid parameters and antioxidant enzymes) of broilers under heat stress. However, 200mg/kg was more effective than 100mg/kg.