The seasonal variation of essential oil composition of aerial parts and roots of Artemisia absinthium L. has been investigated. It was obtained from individuals growing wild in Teruel (Spain) by means of hydrodistillation (aerial parts) or simultaneous distillation extraction (roots), and analyzed by GC/MS and GC/FID. Results showed a predominance of oxygenated monoterpenes (81.4â89.1%) in aerial parts; mainly (Z)-epoxyocimene (49.3â71.5%), (Z)-chrysanthemyl acetate (7.6â18%) and linalool (0.7â10.4%). In spite of the high intrapopulational variability, significant variations were observed for these three compounds. Root essential oil composition showed a high amount of hydrocarbon monoterpenes (43.8â55.1%) and monoterpenic esters (36.6â41.5%) with a noticeable seasonal stability except for some allelopathic oxygenated monoterpenes. As A. absinthium is a typical invasive species, knowing the seasonal variations of these compounds may be a first step to study their release in soil as a source for natural herbicides.