BACKGROUND: Vitamin C and Carum copticum with antioxidant activity may eliminate the negative effects of heat stress on broiler performance and immunity.OBJECTIVES: This experiment was conducted to investigate the effect of feeding heat-stressed broilers with Carum copticum seed powder (CSP) and vitamin C (VC) on their growth performance, blood metabolites, carcass characteristics, and meat quality.METHODS: Herein, we carried out A 2*3 factorial arrangement in a completely randomized design with six treatments, including three levels of CSP (0, 0.75 and 1.5 % of diet), two levels of VC (0 and 250 mg/kg of DM of diet), and four replicates, on 240 one-day-old male Ross 308 broilers. The collected data were analyzed using PROC GLM of SAS. Treatment means were compared employing the Tukey test.RESULTS: The effect of CSP on their performance was not significant whereas VC treatment improved weight gain significantly (P<0.01). Interaction of CSP and VC on weight gain and feed conversion ratio was significant as broilers fed with 250 mg VC and those fed with 1.5 % CSP had the best WG and FCR (P<0.01). The addition of VC decreased the concentration of alkaline phosphatase in the blood (P<0.05). The heterophil to lymphocyte ratio was reduced through the use of VC and 1.5 % CSP (P<0.05). CSP supplementation at the rate of 1.5 % increased the relative weight of bursa of fabricius (P<0.05). Dripping loss percentage was reduced in birds fed with 1.5 % CP and VC (P<0.01). The effect of CSP and their interaction on water holding capacity was significant and the highest amount belonged to the birds fed with 1.5 % CSP (P<0.01). Additionally, VC increased meat ash percentage compared to the control group (P<0.01).CONCLUSIONS: The results of this study indicated that addition of 250 mg VC and 1.5 % CSP could be conducive to improving growth performance, blood metabolites, and meat quality of broilers under heat stress conditions.