Heat shock protein 70 (Hsp70) is one of family of proteins expressed in response to a wide  range of biotic and abiotic stress conditions. Quantitative real-time PCR (qRT-PCR) has been used to study the expression profiles of heat shock protein (Hsp70) gene in Nile tilapia, Oreochromis  niloticus. Young fish (30 g) were exposed to  different degrees of heat (10, 15, 35, 39) and control (28°C) for 2 and 4 hr., followed by qRT-PCR of Hsp70 mRNA, using Beta actin (ß-Actin) as a reference gene and flourogenic dyes. Expression of Hsp70 gene  was different  among fish tissues (muscles, gills and liver). In all treatments the expression level detected in male were more than female fish. The highest expression organs after 2 hr., was muscles in both fish sex but after 4 hr.,  liver recorded the highest expression value at cold shock where muscles recorded the highest expression at heat shock treatments in both fish sex.