Variation in the quantity and quality of the essential oil of Artemisia annua L. (Asteraceae) at different developmental growth stages including pre-flowering, flowering and post-flowering, are reported. The oils were obtained by hydro distillation of the air-dried samples. The yields of oils (w/w %) in different stages were in the order of: pre-flowering (0.97%), flowering (1.23%) and flowering (0.87%). The oils were analyzed by gas chromatography-mass spectrometry. In total, 32, 35 and 33 constituents were identified and quantified in the oil of pre-flowering, flowering and post-flowering plants, representing 97.67, 92 and 92.4 % of the oils, respectively. Camphor, 1,8-cineole, camphene, spathunelol, α-pinene and artemisia ketone were the main compounds in all samples. Monoterpenes were the main group of compounds in pre-flowering (69.96%), flowering (72.44%) and post flowering (70.96%) stages.