The Rosmarinus officinalis (rosemary) is an evergreen shrub used worldwide for its aromatic and medicinal virtues. It plays an important role in the local economy of Talsint (Eastern Morocco). Even though, forest managers and decision makers are short of information and scientific indicators to accurately understand how the chemical composition of rosemary varies in the region. Hence, the aim of this work is to study the effect of altitude gradient over the chemical composition of the rosemary essential oil and its antioxidant activity. In this study, eight samples of wild population of rosemary were collected from different altitudes in the High Atlas Mountains in the region of Talsint in order to determine the chemical composition and antioxidant activity of their essential oils. The volatile profiles were determined by Gas chromatography–mass spectrometry (GC-MS), meanwhile, the antioxidant activity to scavenge the free radicals was pointed out by 1,1- diphenyl-1-picrylhydrazyl (DPPH) assay. Based upon our analysis, the major constituents are 1,8-Cineole (50.60-64.27%), Camphor (1.77-14.12%), α-Pinene (6.61-9.02%), and Borneol (1.98-6.20%). Except the 1,8-Cineole, the altitude effect remains unclear for the other constituents. On the other hand, the essential oils of Talsint rosemary showed considerable antioxidant activity
