The extraction of essential oil was carried out using two processes: hydrodistillation and supercritical CO 2 extraction. The chemical composition of extracted essential oil was determined. The yield of extraction by supercritical CO 2 was about 7.8 %. This yield is more important than that obtained by hydrodistillation process (5.51 %). The chemical composition of the supercritical CO 2 extract indicates the presence of only two compounds. The major one is undecan-2-one (100 %). The second one is limonene which is present as trace. However, 23 compounds were identified in the essential oil of the aerial part of Ruta chalepensis extracted by hydrodistillation process. The major compound is also undecan-2-one (77.7 %).can be done by supercritical CO 2 6, 7, 8, 9,10,11,12,13,14,15 . The process uses supercritical carbon dioxide (CO 2 ), which under some conditions of pressure and temperature, behaves as a solvent. This process allows to work at a moderate temperature (31°C), which does not alter the organoleptic quality of the extracts obtained 16 . At the end of the extraction, by pressure reduction (relaxation), induce the passage of CO 2 in the supercritical state to the gaseous state and the CO 2 is removed from the extract alone under atmospheric pressure. Generally, supercritical CO 2 can solubilize non polar compounds and low molecular weights. Due to its low critical temperature (Tc = 31°C), CO 2 is leading industrial supercritical fluids: it allows developing processes for low temperature sensitive products. Its density at Tc = 31.1°C and Pc = 73.8 bar (pressure) is about 0.47 g/cm3. The most important parameters in the extraction by supercritical CO 2 is the amount of extract obtained relative to the amount of CO 2 consumed (kg extrait/kg CO 2 ) and the amount of CO 2 consumed relative to the amount of plant material processed (kg CO 2 /kg plant material) 6 .Indeed, Ruta species are resources of various classes of natural products with biological activities: antifungal, antioxidant, phytotoxic, abortifacient, antidepressant, antidote, antiinflammatory 36,37,38,39,40,41,42,43,44 . The undecane-2-one is organic liquid oil produced synthetically. It can also be extracted from species of Ruta. It is also found naturally in bananas, clove, strawberry etc. 45 . The undecane-2-one is used in the perfume and aromatic industry, but thanks to its strong odor is used as a repellent of insects or animals. Typically 1-2 % concentration undecane-2-one as a liquid, aerosol or gel is considered repellent for dogs and cats 46 . 1. Rezzoug, S.A., Boutekedjiret, C.,Allaf, K. (2005). Optimization of operating conditions of rosemary essential oil extraction by a fast controlled pressure drop process using response surface methodology. Journal of Food Engineering, 71: 9-17. 2. Reverchon, E. (1997). Supercritical fluid extraction and fractionation of essential oil and related