The medicinal plants play a major role and constitute their backbone in almost all the traditional systems of medicine. The focus on medicinal plants is increased in past few years. In this book, estimation of chlorophyll content, antioxidant potential, measurement of growth by different physical parameters and separation of phenolic compounds of selected medicinal plants were done by using reverse phase high pressure liquid chromatography (RP-HPLC). The main objectives of this study are (1) To understand, at which stage the selected medicinal plans have maximum antioxidant activities and the probable phenolics that may have key role in antioxidant activity of the different stages of the leaves; and (ii) To measure antioxidant activity and to separate the phenolics from selected medicinal plants by using RP-HPLC.