The present study was undertaken to test the effect of heat stress (39 °C) for 4 hours on Hsp70 mRNA profiling in two chicken genotypes. Expression levels of hsp70 were used to assess the heat tolerance of two Egyptian local genotypes (Fayoumi and Matrouh). The expression level of the hsp70 gene is high in the Fayoumi type as opposed to the Matrouh type. In blood, after four hours of exposure, the hsp70 mRNA expression analysis revealed higher expression levels. These results showed that the acquired thermotolerance is positively linked to the stress memory. Within the two genotypes, Fayoumi type exhibited the highest means for hsp70 production, and therefore the heat stress is better tolerated, which indicates that Fayoumi mortality rate might be lower genetically under heat stress