The chemical compositions of essential oils from the roots of Erigeron acris and Erigeron annuus were studied. The essential oils were obtained by hydrodistillation in 1.0% and 0.05% yield, respectively, and analyzed by GC, GC-MS. Fifty four and forty seven constituents were identified. Predominant constituents of both oils were poly-acetylene esters: (Z,Z)-matricaria ester (49.4% and 45.9%, respectively) and (Z)-lachnophyllum ester (37.2% and 27.5%, respectively), that were accompanied by their stereoisomers as well as appropriate lactones. Polyacetylenic compounds amounted to 92.1% of E. acris oil and 85.8% of E. annuus oil. Both oils contained the same monoterpene hydrocarbons, amounting to 4.2% and 5.8%, respectively, and traces of almost the same monoterpene oxygenated compounds. The dominant sesquiterpenes in E. acris were elemenes and tricyclic sesquiterpene hydrocarbons, while in E. annuus beta-sesquiphellandrene and beta-bisabolene dominated. After flash chromatography of essential oil from E. acris, fractions contained acetylene esters and acetylene lactones were obtained. The configuration about double bonds for these compounds has been elucidated on the basis of (1)H- and (13)C-NMR analysis.