Plantology studies showed that,there are more than 1200 Plant Species that they have hypoglycemic properties.Stevia Rebaudiana bertoni is the best of the them. The value of this plant is the because of steviol glycosides content in It"s leaves. Stevioside and Rebaudioside A are two main glycosides compounds of Stevia. However, Rebaudioside A is the most sweetest steviol glycoside in Stevia. It dose not have any colory,therefore it has known as hyperglycemic drouge. Because of our country Iran, has placed in drought region ,we induced drought stress on stevia for detection effect of the drought stress on the expression of three genes involved in the glycosides biosynthesis pathway of steviside to rebaudioside A. At first time, we extracted RNA from leaves,with CTAB method and then synthesised cDNA with fermentase cDNA synthesis kite. After, by RealTime-PCR technic,we studied the expression of thease genes(UGT74G1,76G1,85C2).Finally,by analysis of data result from RealTime-PCR,UGT76G1gene,was detected, as main gene of biosynthesis pathway of stevioside to rebaudioside A.