Abstract Twenty-six samples of Thymus serpyllum ssp. serpyllum were collected from 14 habitats in Lithuania and the composition of their essential oils were analyzed by capillary gas chromatography (GC) and GC/MS. The study revealed remarkable infraspecific variation in the oil composition. Five main groups of the plants were observed using hierarchical cluster analysis based on the major essential oil constituents. Consequently, five chemotypes of T. serpyllum have been defined, namely 1,8-cineole, germacrene B, (E)-β-ocimene, α-cadinol and cis-p-menth-2-en-1-ol. It was concluded that there is no clear relation in the oil composition between the studied varieties and chemotypes. Two chemotypes were defined within the ssp. serpyllum var. serpyllum, two chemotypes within the ssp. serpyllum var. lineatus, and one chemotype within ssp. serpyllum var. rigidus. Key Word Index: Thymus serpyllum ssp. serpyllum Lamiaceaeessential oil compositionl-octen-3-olmyrcene1,8-cineole(Z)-β- ocimene(E)-β-ocimene cis-p-menth-2-en-1-olcamphorborneolα-terpineol cis-dihydrocarvoneβ-caryophyllenegermacrene Dgermacrene Bd-cadineneb-bisabolenecaryophyllene oxidea-cadinolchemotypes