Detrimental effects of heat stress that causes great loss to poultry industry have grown the global attention for the importance of natural antioxidant in alleviating the oxidative stress symptoms in poultry. The antioxidant effect of Chinese ether extract propolis (EEP) on broilers (Ross 308) exposed to chronic heat stress has been evaluated. Eighty broilers (15 days old) were randomly allocated into five equal groups; each received a maintenance diet supplemented by vitamin C (250 mg/kg diet) or propolis (250, 500 and 750 mg/kg diet) or not supplemented (control) for 27 consecutive days. Blood samples were collected to analyze serum corticosteron, total antioxidant capacity (TAC) and lipid peroxidation activity (MDA) at the end of the experiment. Moreover, the active chemical components responsible for the biological activities of EEP have been determined using Gas Chromatography/Mass Spectrometry (GC/MS). Results revealed a significant decrease in corticosterone levels in broilers after vit C or EEP supplementation. This improvement is parallel to a significant increase in TAC and decrease in MDA in broilers after EEP supplementation, which may be due to its high flavonoid content. Results show that Chinese EEP has biologically active compounds responsible for excellent antioxidant activities that ameliorate the negative impacts of elevated temperature in summer season in Egypt.