In this study, the extraction of Glycyrrhizic acid (GA) from Glycyrrhiza glabra (licorice) root was investigated by Soxhlet extraction and modified supercritical CO2 with methanol and water as co-solvents and 30min of static time. Design of experiment was carried out with response surface methodology (RSM) using Mini Tab software 17. The operating temperature (45-85 degrees C), pressure (10-34 MPa), dynamic extraction time (40-120 min), CO2 flow rate (0.8-2 ml/min) and methanol concentration in water (0-100% as the binary co-solvent) were considered as the range of operating variables. The high performance liquid chromatography (HPLC) was used to identify and quantitatively determine the amount of extracted GA. Response surface analysis verified that R-2 and modified R-2 of the model were 98.05% and 94.51%, respectively. The RSM modeling predicted the optimal operating conditions to be the pressure of 29.6 MPa, temperature of 68 C, CO2 flow rate of 2 ml/min, dynamic extraction time of 108 min, methanol concentration of 46.5% in water (v/v) in which the maximum recovery of 54A% was obtained. The accuracy of the modeling optimal GA recovery was validated with triplicate experiments giving the average extraction recovery of 54 1%. (C) 2015 Elsevier B.V. All rights reserved.