10.22376/ijpbs.2019.10.1.p1-12 Volume 3 Issue 1 2012 (January - March) Ethylene is a gaseous plant hormone that affects numerous developmental processes and fitness responses, including germination, flower and leaf senescence, fruit ripening, leaf abscission, programmed cell death, and responsiveness to stress and pathogen attack. This hormone can significantly increase seed germination of some medicinal plants such as Purple coneflower. A number of investigators have added ethylene to plant cell cultures to enhance the yield of desired compounds of medicinal plants like phenolics and flavans. Berberine was produced in suspension cultures of lessThan i greaterThan Thalictrum minus lessThan /i greaterThan and enhanced by addition of ethrel. Production of purine alkaloids was influenced by application of ethylene in Coffe. Silver ions are capable of generating ethylene insensitivity in plants. Silver nitrate not only induced shoot multiplication but also influenced rooting of vanilla explants. Ethylene can affect dry matter of stem, leaves and flowers of some medicinal plants. Lavandin Shoot formation was inhibited by addition of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, indicating an involvement of ethylene in the failure of regeneration. Ethylene, a natural ripening hormone, is used to synchronize chilli ripening to make mechanical harvesting possible. Yield and components of essential oils were affected by ethylene. This review focuses on effect of ethylene on growth and active substances of some medicinal plants. Shahram Sharafzadeh plant hormone, essential oils, secondary metabolites, ethephon 465-469