Essential oil leaves of nine Tunisian Thymus capitatus populations, growing wild in six bioclimatic zones, were analyzed by gas chromatography–mass spectrometry (GC–MS). The species was found to be rich in oxygenated monoterpenes (76.9%-84%) followed by monoterpene hydrocarbons (11.6-15.3%). The main component of the essential oils was the carvacrol (73–82.9%). Cluster analysis performed on major compound contents did not reveal clear groupings of populations according to their bioclimatic zone.

The species essential oils were assessed for their anti-acetylcholinesterase activity. The level of biological activity of the populations was linked to their chemical composition difference. The most important activity was observed for populations Tc2 and Tc8 from the upper semi-arid and upper arid bioclimatic zone, respectively, characterized by the highest carvacrol level. The best activity was revealed for the standard carvacrol. A significant correlation between anti-acetylcholinesterase activity and carvacrol was revealed.