Abstract The quantitative composition of the essential oils from several subspecies, varieties and populations of Sideritis pusilla (Lange) Pau (Lamiaceae), analyzed by GC and GC/MS, is reported. Monoterpene hydrocarbons, alcohols, sesquiterpenes and diterpenes were the main constituents in all samples. Among these, Î±-pinene (7.1â25.4%), sabinene (5.9â20.4%), fenchone (0.9â19.3%), limonene (1.2â7.4%) and 1,8-cineole (1.8â15.6%) were the major compounds. The results confirm that there are differences between varieties and subspecies, while cluster analysis revealed that the oil composition potentially has chemotaxonomical significance for this taxon. Key Word Index: Sideritis pusilla ssp. oxteoxylla Sideritis pusilla ssp. almeriensis Sideritis pusilla ssp. pusilla Sideritis pusilla ssp. flavovirens Lamiaceaechemotaxonomyessential oil compositionÎ±-pinenesabinenefenchone1,8-cineole