This study was investigated the chemical composition from Syneilesis palmata essential oil and the tendency of variation of the sesquiterpene compounds according to the harvesting time. The essential oils obtained by hydro distillation from the aerial parts of Syneilesis palmata were analyzed by GC and GC-MS. Ninety-eight compounds consisting of 9 aliphatic hydrocarbons, 17 sesquiterpene hydrocarbons, 11 aliphatic aldehydes, 1 terpene aldehyde, 8 aliphatic alcohols, 4 monoterpene alcohols, 16 sesquiterpene alcohols, 3 diterpene alcohols, 6 ketones, 11 esters, 8 oxides and epoxides, 3 acids and 1 miscellaneous one were identified from the oil. Spathulenol (22.33%) was the most abundant compound, followed by ${eta}$- caryophyllene (6.23%), germacrene D (5.57%), longipinane (4.10%), and epiglobulol (3.65%). The volatile composition of Syneilesis palmata was characterized by higher contents of sesquiterpene compounds, especially sesquiterpene alcohols. The total content of 13 sesquiterpene compounds was decreased significantly from 2010 to 2012. ${alpha}$-Caryophyllene, ${eta}$-bisabolene, elemol, germacrene D, ${eta}$-zingiberene, longipinane, and ${eta}$-caryophyllene alcohol contents decreased, while ${eta}$-bisabolol content increased during 3 years. The ecological responses to recent climate change may be influenced in the chemical components of natural plant terpenoids.