The aim of this study was to optimize the percentage yield and percentage radical scavenging activity (RSA) of hawthorn leaf/flower (fol/flos = FF) and hawthorn berries (fructus = Fr) using supercritical carbon dioxide as the extraction technology. Response surface methodology was employed, using a Bex-Behnken statistical design to evaluate the effects of three independent variables. Pressure (100-400 bar), temperature (40-60 degrees C) and modifier (ethanol) concentration [no modifier (0%), 45%, 90%] were the three variables with total extraction time and CO2 flow rate being held constant at 35 min and 5 L/min, respectively, for each extraction. Antioxidant activity was measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Optimal extraction conditions, as predicted by response surface methodology were; pressure of 400 bar, temperature of 50 degrees C and use of no modifier for hawthorn leaf/flower and, pressure of 310 bar, temperature of 60 degrees C and use of no modifier for hawthorn berries. (C) 2013 Elsevier B.V. All rights reserved.