The objective of this study was to evaluate the effect of harvest at different times on the chemical composition of phenolic compounds of Artemisia herba-alba. Plant material has been harvested at three times (July, November, and May). Methanolic plant extracts were obtained by means of ultrasound-assisted extraction and then analyzed by HPLC-electrospray ionization-Q-TOF-MS for their phenolic profile. The HPLC allowed the identification of 26 phenolic compounds, 12 of them were identified for the first time for this material. The phenolic compounds detected were 8 phenolic acids, 12 flavones, 4 isoflavone, 1 flavonol, and 1 flavanone. Results showed that during the all harvesting date, phenolic acids were predominant. In November, at the flowering period, it revealed the highest accumulation of total phenolic contents (515 ± 142 mg GAE/g dry matter weight [DMW]) in the methanolic extracts. November at the flowering period was characterized by the highest levels of flavonoids 8.3 mg/g DMW and the lowest contents of phenolic acids 3 mg/g DMW. ARTICLE HISTORYArtemisia herba-alba; Flavonoids; phenolic acids; high-performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flightmass spectrometry CONTACT Touil Souhila