Aromatic plants can interfere in the Mediterranean ecosystem, mainly by the introduction in the environment of volatile compounds. For this reason, we studied the chemical composition and the possible phytotoxic and antimicrobial activities of the essential oil extracted from leaves of Tunisian Artemisia herba-alba Asso. The chemical composition of the essential oil, obtained by hydrodistillation, was analyzed by GC and GC-MS. In all, 24 compounds were identified. The main components were camphor (39.1%), chrysanthenone (15.0%) and cis-thujone (7.8%). The essential oil was evaluated for its in vitro phytotoxic activity against germination and initial radical growth of Raphanus sativus L., Lepidium sativum L., Sinapis arvensis L., Triticum durum L. and Phalaris canariensis L. seeds. The radicle elongation of the five seeds was affected to different extents by the oil, while germination was not affected. The oil, when tested against eight selected bacterial strains, showed low antimicrobial activity. The chemical composition of the oil of A. herba-alba can help in the chemosystematics of this complex genus. However, the recorded biological activities seem to be neither ecologically nor medicinally significant.