AIM To prepare the hydroxypropyl-β cyclodextrin inclusion compound of volatile oil from Houttuyniae Herba.METHODS In the content determination of volatile oil by GC,2-undecanone was taken as a reference substance,and inclusion rate and drug loading were calculated.After the determination of optimal method for preparing the inclusion compound among techniques of mixing,grinding and ultrasonic methods.the preparation process was optimized by orthogonal test with ratio of volatile oil to hydroxypropyl-β cyclodextrin,inclusion temperature,mixing speed and inclusion time as influencing factors,and inclusion rate and drug loading as evaluation indices.The characterization was performed by TLC,infrared spectroscopy and differential scanning calorimetry.Then high temperature,high humidity and strong light tests were applied to investigating the inclusion compound stability.RESULTS Mixing method brought forth the maximal yield,inclusion rate and drug loading for the inclusion compound.And under the optimal conditions of 1 ∶ 25 for ratio of volatile oil to hydroxypropyl-β cyclodextrin,50 ℃ for inclusion temperature,420 r/min for mixing speed,and 80 min for inclusion time,the inclusion rate and drug loading were identified to be 77.35％ and 4.48％,respectively.The obtained inclusion compound was found to be white powder with loose texture and significantly increased solubility,the in vitro accumulative release rate reached 80.85％.Deliquescence and agglomeration,as well as obviously decreased inclusion rate and drug loading,were observed at a relative humidity of more than 75％,despite the good stability at high temperature (60 ℃) and strong light (3 000 lx),and yet the rehydration character was good.CONCLUSION It is possible that the hydroxypropyl-β cyclodextrin inclusion compound of volatile oil from Houttuyniae Herba generates a new phase rather than a simple mixture,which should be kept dry and sealed at the time of storage.