The objective of this study was to estimated gene expression in breast muscles of two broiler strains with used to Myoustatin gene in marketing age (5 weeks of age) under heat stress and compared to control group for 1 hour daily for 7 days in Shalakan farm of Faculty of Agriculture, Ain Shams University, broiler chicks (150 chicks in each strains) of 1 day of age were used in this study. So, the measurements were taken (respiratory rate, rectal temperature and estimated gene expression). The results obtained the gene expression of Myostatin gene in muscle breast was observed highest in Ross strain compared with Indian River strain under heat stress, but no different between strains ( Ross and Indian River) in control group. However, respiratory rate of Ross and Indian River under heat at 5 week of age showed that the Indian River strain was high significant at 5 week of age compared to Ross ones. As shown that rectal temperature of Ross and Indian River were a high significant effect of treatment (heat group was higher from control group) and not a significant of strain.The present experiment was conducted to estimated gene expression on meat quality traits of different tropical stress conditions in different broiler strains during 7 days and 5 weeks of age. Introgressions some major genes likes myostatin gene in muscle breast into broiler improve under the heat stress.