本研究旨在由天胡荽與雷公根抽取出之精油成分做比較探討，首先在天胡荽部分抽取出之精油成分有三十四種而在雷公根部分抽取出之精油成分有十九種，經比對天胡荽與雷公根抽取出之精油成分共有十種相同：p-Cymen-8-ol、Phytol、β-Elemene、Hexahydrofarnesylacetone、α-Humulene、β-Farnesene、β-Eudesmene、α-Selinene、Caryophyllene oxide andβ-Caryophyllene，並比較兩者利用水蒸氣蒸餾在抽取過程中所萃取得到的全精油成分的收油率分別為0.211 ％與0.046 ％。 The purpose of this research was to compare the constituents of essential oil extracted from Hydrocotyle sibthorpioides Lam. and centellaasiatica ( L.) Urb., respectively. First, thirty-four essential oil compounds from the extract of the Hydrocotyle sibthorpioides (Lam.) and ninteen essential oil compounds from the extract of the Centella asiatica (L.) Urb. were identified, respectively. The constituents from the essential oil of both plants contained the sarne ten compounds : p-Cymen-8-ol、Phytol、β-Elemene、Hexahydrofarnesylacetone、α-Humulene、β-Farnesene、β-Eudesmene、α-Selinene、Caryophyllene oxide andβ-Caryophyllene. The essential oil was extracted from both plants by steam distillation, and the amount of the neutral essential oil collected was about 0.211% and 0.046% , respectively.