Antioxidant effects of vitamin A and zinc element is highly regarded under heat stress. Current study was carried out to investigate the effects of different levels of vitamin A and zinc on performance, thyroid hormones of broilers under heat stress. In this study, 420 broilers were evaluated in six treatments and five replications in a completely randomized design. Treatments were 1: 100000 IU of vitamin A plus 100 ppm of zinc per kilogram of diet, 2: 100000 IU of vitamin A plus 150 ppm of zinc per kilogram of diet, 3: 100000 IU of vitamin A plus 200 ppm of zinc per kilogram of diet, 4: 200000 IU of vitamin A plus 100 ppm of zinc per kilogram of diet, 5: 200000 IU of vitamin A plus 150 ppm of zinc per kilogram of diet,6: 200000 IU of vitamin A plus 200 ppm of zinc per kilogram of diet. To enforce the heat stress, temperature was increasing daily to 35° C eight hours a day. Venous blood was used to measure thyroid hormones. According to results, at 42nd day, T4 and T3 were significantly affected by treatments. T4 amount of group 1 was significantly less than other group and significant differences were between T3 of group 1, 2 and 6. Considering the results, interaction effect of vitamin A and zinc supplement completely depends on their concentrations in diet and can be considered as an important factor for thyroid performances.