Twenty-one accessions of Ocimum basilicum belonging to two different varieties in Iran (var. purpurascens and var. dianatnejadii) were subjected to a chemical characterization of essential oil components by gas chromatography/mass spectrometry (GC/MS) and identify the different possible chemptypes of studied accessions. Altogether, 49 compounds were identified in the oils that accounting for 96.6-99.7% of the total oils. The main constituents of the essential oils were methyl chavicol (33.6-49.1%) and linalool (14.4-39.3%) that indicating they were the common compounds in the varieties of O. basilicum and the essential oils of the 21 accessions chiefly consisted of aromatic and oxygenated monoterpene compounds. The essential oil components except two main constituent those which comprised 20% or more of the total, were especially variable in occurrence and concentration among the different accessions, ranging from absent in some varieties to more than 4% of the total essential oil composition in others. Monoterpene hydrocarbon compounds were presented in the essential oil of all accession of purpurascens variety and didn’t identify in those of related to var. dianatnejadii, indicating that monoterpene hydrocarbons could be considered as the marker constituents of purpurascens variety. To investigate the chemical variations of essential oils in different accessions of O. basilicum L., the composition data were analyzed by cluster analysis. The cluster analysis showed a clear separation of O. basilicum var. purpurascens and O. basilicum var. dianatnejadii, but these date did not show chemotype variation in studied accessions. In conclusion, GC/MS in combination with chemometric techniques could provide a flexible and reliable method for characterizing the chemical profiles of different varieties of Ocimum basilicum L.

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