Two hundred and forty 1-d old commercial broiler chicks (Cobb) were allotted to two groups of 120 chicks. The first group was the control(Non heat conditioning). The second one was exposed to 40±1°C for 24h at 5 DOA, (early age heat conditioning). Each group was further subdivided into 4 sub-groups of 30 birds each, the first sub-group was control group,  the second was fed basal diet supplemented with 200 IU/kg diet vitamin E and 0.8 mg/kg diet chromium methionine, the third was fed basal diet supplemented with 200 IU/kg diet vitamin E and 0.3 mg/kg diet selenium methionine and the fourth was fed basal diet supplemented with 200 IU/kg diet vitamin E, 0.8 mg/kg diet chromium methionine  and 0.3 mg/kg diet selenium methionine, to investigate the effects of early age of heat conditioning and some antioxidants supplementation on somephysiological changes. Results showed that Chicks exposed to early age heat conditioning recorded significantly higher (P< 0.05) BW, BWG, FI and FCR compared with non heat conditioning chicks at 21and 42 DOA. There were significant (P<0.05) effects of dietary supplements on BW, BWG, FI and FCR at 21 and 42 DOA, and also by the interaction between early age heat conditioning and dietary supplements. Early age heat conditioning had significant (P< 0.05)  effect on Hb, HT, RBC´S, MCHC and MCV levels at 21 DOA, but MCH values was insignificantly influenced. Significant (P< 0.05) effects of early age heat conditioning significant (P< 0.05) effects on Hb, HT, and RBC´S levels of broiler chicks at 42 DOA, however, MCH, MCHC and MCV levels were not affected. Dietary supplements (regardless early age heat conditioning) significantly increased Hb, HT, RBC´S, MCH, MCHC and MCV levels at 21 DOA and at 42 DOA except MCH, MCHC and MCV which were not significant. The interaction between early age heat conditioning and dietary supplements was significant for most of the hematological parameters studied either at 21 or 42 DOA. Early age heat conditioning had a significant (P< 0.05) effect on H/L ratio, but the effect of dietary supplements alone was not significant at 21 and 42 DOA. Based on the results of the present study it is concluded that early age heat conditioning of broiler chicks and dietary supplements by Vit.E; organic chromium or organic selenium in combination could be recommended for alleviating the negative effects of heat stress during the summer season, on broiler chicks performance.