A total of 225 7-day-old Ross 308 chicks were randomly assigned to nine groups consisting of 25 birds each. In a completely randomized design, each treatment was repeated 5 times with 5 chicks. The following diets were used as treatments: providing merely a basic meal without additives and acting as a control group,, the 2^nd and 3^rd were received basal diet supplemented with Chromium-l-methionine complex (Cr-Meth) at a dose 0.3 and 0.4 gm/kg diet, the 4^th and 5^th were received basal diet supplemented with peppermint oil (PO) at a dose 0.6 and 0.8 gm/kg diet, while 6^th, 7^th, 8^th and 9^th were given the basal diets supplemented with a combination of Cr-Meth (0.3 and 0.4 gm/kg diet) and PO (0.6 and 0.8 gm/kg diet), respectively.  The results showed that the best values of body weight, body weight gain, feed intake and feed conversion ratio were recorded in T7, T9, T3 and T8, respectively. The relative weights of gizzard, liver, heart, and spleen were non-significantly (P≤0.05) affected expect relative weight of bursa and abdominal fat which were significantly (P≤0.05) affected by tested materials and their mixture. Different additives added alone or in combination significantly (P < 0.01) reduced serum total cholesterol and triglycerides.  Exposing birds to high temperature conditions resulted in elevated (P ≤ 0.05) serum malondialdehyde as presented in the control one, however, it was significantly decreased by all dietary treatments. Besides, numerical increase in serum total antioxidant capacity was observed due to supplementation of different feed additives. In conclusion, dietary inclusion of Cr-Meth and PO could be applied as an antioxidants in broiler chicks' diets under heat stress conditions.