The Brassicaceae, which has about 350 genera and 3500 species, is one of the ten most economically important plant families [1]. The plants display enormous diversity and are used as sources of oil, vegetables, mustard condiments, and fodder [2].The genus Erysimum belongs to the Brassicaceae family. The Iranian Flora consists of 25 species of Erysimum, including 13 endemics, and the popular Persian name of the species is "Khakshir-e-Talkh" [3]. Erysimum crassicaule Boiss. is a biennial plant distributed in Iran and Pakistan [3,4].A literature search did not reveal any references to previous work on the essential oils of Erysimum species. The present work studies the chemical composition of the essential oil from the aerial parts of E. crassicaule for the first time.The plant material was collected during the flowering stage from Rayen (at an altitude of 2900-3000 m) Kerman Province, Iran in May 2013. A voucher specimen (No. 8522) has been deposited in the Herbarium of the Research Center of Agriculture and Natural Resources of Kerman, Iran. The air-dried aerial parts of the plant (200 g) were crushed and subjected to hydrodistillation for 3 h using a Clevenger-type apparatus. The yield of the essential oil was 0.2% (w/w) relative to the dried material.The constituents of the oil were analyzed by GC and GC/MS. GC analysis of the volatile components was carried out using a Hewlett-Packard 6890 instrument coupled to a flame ionization detector (FID). Compounds were separated on an HP-5 capillary column (30 m u 0.25 mm, film thickness 0.25 Pm). The column temperature was kept at 60qC for 3 min and programmed to 220qC at a rate of 5qC/min. Injector and detector temperatures were 270qC, and the flow rate of helium as carrier gas was 1 mL/min. The percentage composition of the individual components was computed from the GC-FID peak areas without the use of correction factors. GC/MS analysis was performed using an Agilent 5975C mass spectrometer coupled to an Agilent 7890A gas chromatograph equipped with an HP-5MS capillary column (30 m u 0.25 mm, film thickness 0.25 Pm). The carrier gas was helium, and the chromatographic conditions were as above. All mass spectra were acquired in electron-impact (EI) mode. The spectrometer was scanned over the 40-400 amu range with an ionization voltage of 70 eV and an ionization current of 150 PA. Retention indices were determined using the retention times of n-alkanes, injected after the essential oil under the same chromatographic conditions, according to the Van Den Dool method [5].The chemical compounds, which were identified on the basis of their mass spectral characteristics and retention indices [6,7], are listed in Table 1. As is shown, 13 components were identified in the essential oil, amounting to 100% of the total volatiles. The chemical class distributions of the volatile constituents are summarized at the end of Table 1. Based on the analysis of the oil, the components were classified in four groups as follows: phenylpropanoid derivatives, oxygenated monoterpenes, sesqui...