Catharanthus roseus (L.) G. Don is a medicinal plant rich in many alkaloids that are used in treatment of many diseases. It is unique in the production of vinblastine and vincristine compounds, which are used in treatment of several cancers. There are many genes in the biosynthesis pathway that produce these anti-cancer compounds, including the gene Crwrky1 which is a regulatory gene that codes for the transcription factor in the monoterpene indole alkaloid (MIA) pathway. In this study, the effect of yeast extract on crwrky1 gene expression levels from treated calli was studied. Quantitative RT-PCR (QRT-PCR) using SYBR Green I/ROX was used to analyze the changes in the expression level of this gene in response to different treatments of yeast extract. Crwrky1 expression increased to 3.6 folds in treated callus obtained under 0.4 mg/l yeast elicitor for 4 hours (YE2) treatment to compare with the control (untreated) callus.