The present study deals with the determination of optimal values of operating parameters such as temperature and pressure leading to the best yield of a supercritical CO2 extraction of essential oil from local rosemary plants, using the response surface methodology (RSM). The maximum of essential oil recovery percentage relative to the initial mass of leaf powder was 3.52 wt%, and was obtained at 313 K and 22 MPa. A second-order polynomial was used to express the oil recovery and the calculated mass of recovered oil using the RSM was very close to the experimental value, confirming the reliability of this technique. The chemical composition of the Algerian rosemary oil under the obtained optimal conditions (313 K and 22 MPa), determined by GC-MS analysis, revealed the presence of camphor (major compound) (52.12%), 1,8-cineole (9.65%), camphene (7.55%), alpha-pinene (6.05%), borneol (3.52%), aroma dendrene (2.11%), verbenone (1.97%), alpha-caryophyllene (1.71%), and others. (C) 2016 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.