The investigation is involved with the development of the new method of decoction preparation in order to prevent the loss of volatile oil from crude drugs. Volatile oil in crude drug containig volatile oil ranged from 1 to 2.2% in content. Volatile oil content in crude drung prescription which main component is a crude drug containing volatile oil was $0.11{sim}0.39;ml$. It was found that traditional method of decoction preparation has caused to lose almost all of the volatile oil. Application of method of Pharmacopoea (Kp II) for the preparation of decoction prevented the loss of volatile oil from one half to two-third of its content. The method of Pharmacopoea to which air condenser was attached could completely prevented the loss of volatile oil from the preparation.