This study aims to determine the effect of thyme essential oil (TEO) and a combination of TEO with different vitamins (A, C and E) on performance, carcass quality, oxidation parameters in broilers exposed to heat stress (HS). A total of 300, 21 days old, male Ross-308 chicks were distributed in six experimental groups with five replicates. The broilers in HS groups were exposed to 34 degrees C for nine hours per day between 21 and 41 days of the experiment. The experimental groups were as follows: 1: Thermoneutral control (TNC, 22 degrees C), 2: Heat stress control (HSC, 34 degrees C), 3: TEO (300 mg/kg TEO, 34 degrees C), 4: TEO + Vit C (300 mg/kg TEO + 250 mg/kg Vit C, 34 degrees C), 5: TEO + Vit E (300 mg / kg TEO + 250 mg/kg Vit E, 34 degrees C) and 6: TEO + Vit A (300 mg / kg TEO + 15000 IU / kg Vit A, 34 degrees C). As a result, it was determined that HS significantly reduced live weight (LW), live weight gain (LWG), and feed intake (FI) values compared to the TNC group (P<0.05). Supplementation of TEO or TEO and vitamin (A, C, E) combinations to the feed of broilers exposed to HS had no significant effect on performance, carcass quality, carcass part yields, and serum parameters. Economically, the highest profitability was obtained in the TNC group (P<0.001), In conclusion, HS negatively affected the performance of broilers, and the supplementation of TEO + Vit E to the diet had slightly reduced the adverse effects of HS.