This experiment was conducted to investigate the effects of dietary supplemental L-ascorbic acid (AA) and folic acid (FA) on broiler chickens under heat stress (HS) conditions when supplemented either alone or in combination. For this aim, the effect of these supplements on the broilers’ growth performance, some blood parameters, antioxidant, and immune status were evaluated. Hatchling Cobb-500 broilers (total = 240) were fed either corn and soybean meal-based diet (control group) or basal diet supplemented with 200 mg AA/kg diet, 1.5 mg FA/kg diet, or 200 mg AA plus 1.5 mg FA/kg diet, for 35 days during the summer months (n = 6 replicates/group, 10 birds/replicate). The minimum and maximum average temperatures ranged from 84.5 to 96.2 °F, and the relative humidity ranged from 68.5 to 76.5%. Supplemented vitamins either alone and (or) in combination increased (P < 0.01) broilers’ growth performance, thyroid hormones levels, insulin growth factor1, blood hemoglobin, total protein, albumin, globulin, heat shock protein70, total antioxidant capacity, catalase enzyme activity, superoxide dismutase enzyme activity, antibody titer against Newcastle disease virus, and decreased (P < 0.01) heterophil/lymphocytes. The effects (P < 0.01) of the supplemented vitamins on the analyzed parameters were better when they were added in combination. In conclusion, the combination of AA and FA at 200 and 1.5 mg/kg, respectively, increased the broilers’ antioxidant status with coordinated improvement in the growth performance and health status under HS.