This study aimed to investigate the impact of a seed mixture (SM) (black cumin, fenugreek, and sesame) on broiler chickens' performance, intestinal morphology, and blood traits under chronic heat stress conditions. 330-day-old male Ross 308 chicks were divided into five treatments (6 replicate and 11 birds per each) consisting of a corn-soybean supplemented with 0, 1.5, 3, 4.5, and 6% SM for 45 days in a completely randomized design. 6% SM supplementation increased BW at 45 days of age, AWG at 26-45 days, and total rearing period under heat stress conditions (P<0.05). Adding 3% SM to broiler diets increased AFI at 26-45 and 1-45 days, FCR at 12-25, and the mortality rate decreased from 28.8% (0% SM) to 12.1% (6% SM) (P<0.05). Adding SM had no significant effects on the relative weight of carcass segments and internal organs (P>0.05) except for the duodenum, was increased weight and length at the level of 6% (P<0.05). The RBC count and Hb were elevated in chicks inoculated with 3% and 6% SM, respectively (P<0.05). MCV value was increased following the supplementation of SM, while differential WBC counts did not influence. AST and ALT activity declined in chicks that received 6% SM at 45 days of age (P<0.05). SM supplementation decreased liver steatosis, uric acid, glucose, total protein, and lipid profile concentration of serum (P<0.05). Therefore, we conclude that adding SM to the broiler diets significantly 6% level improves broiler performance, blood traits, and liver health under chronic heat-stress conditions.