Sesquiterpene having three isoprene units is a kind of terpene , whose general formula is CH, most of them are in line with isoprene rule. Sesquiterpene compounds widely distributed, most abundant in Magnoliales, rue mesh, cornales and asterales (asterales) plants. Generally speaking, sesquiterpene presents in volatile oil in the form of oxygen-containing derivativesthe , such as alcohols, ketones and lactones, the main composition of volatile oil in the high-boiling part , have a strong aroma and biological activity, are pharmaceutical, food, cosmetics important raw material for industry.

Sesquiterpene compounds, in terms of the number or type of structure from the point of view of the skeleton are the largest one in terpenoids. Sesquiterpene are classified by the number of  carbon ring on their structure , for example, acyclic, monocyclic, bicyclic, tricyclic and tetracyclic and so on. Also classified according to the size of the ring, such as five, six, seven till eleven membered ring. If it is classified according to containing group in its structure, it is easy to recognize their physicochemical properties and physiological activities, such as sesquiterpene alcohols, aldehydes, lactones and so on.

The following are some common sesquiterpene compound:
(1) Farnesol ,an open-chain sesquiterpene, presents in aromatic plants volatile oil such as lemongrass, orange blossom, rose and others. Farnesol as a colorless oily liquid, is a valuable spice. having insect juvenile hormone activity. Once the amount of the insect juvenile hormone excess, it will inhibit the insect metamorphosis and maturity.
(2)Germacrone, Aka Big geranylflavanone ketone, presents in the volatile oil of Xing'an azalea (rhododendron) leaves, is a ten-member ring monocyclic sesquiterpene. Rhododendron volatile oil has the effect of treating cough, phlegm, asthma and are useful for the treatment of chronic bronchitis, cuckoo ketone ,whose melting point is 56 ~ 57 ℃,is the main component .
(3) Gguaiazulene. a sesquiterpene ingredients, presents in the tribulus plants guaiac volatile oil, volatile oil Geranium.
guaiazulene. a blue needle crystallization,whose melting point is 31 ℃, has anti-inflammatory effect, promoting wound healing. It is one of the main components of  domestic burn ointment.