Abstract: The volatile composition of two Marrubium species has been studied. The investigated taxa are Marrubium crassidens Bioss. and Marrubium astracanicum Jacp. (Labiatae), which are native in Iran. The essential oils were obtained by hydrodistillation in a modified Clevenger-type apparatus and their analysis were performed by GC and GC-MS. Twenty-two components in the oil of M. crassidens representing 90.5% of the total oil and 24 components in the oil of M. astracanicum, representing 91.9% of the total oil, were identified. Both essential oils were characterizied by a high amount of sesqiterpens with germacrene D (14.2%), bicyclogermacrene (14.2%), β-caryophyllene (29.0%) and spathulenol (5.6%) as the major constituents of M. crassidens and germacrene D (23.4%), α-humulene (33.7%), bicyclogermacrene (11.9%) and spathulenol (6.8%) as the major components of M. astracanicum. Some differences in the essential oil of Marrubium crassidens and Marrubium astracanicum, growing under different environmental conditions, have been found.