Abstract The essential oil obtained from the herb of Erigeron annuus (L.) Pers. harvested at four ontogenesis phases was analyzed by GC, GC/MS and 1H-NMR spectroscopy. More than 60 compounds were identified. Sesquiterpenoids constituted about 90% of the oil. Germacrene D (42.7â63.7%) and Î²-caryophyllene (9.0â15.9%) were the main constituents. The content of germacrene D increased until the flowering stage, however, the content of Î²-caryophyllene decreased at the same time