The xanthones from mangosteen (Garcinia mangostana) pericarp was extracted with and without alcohol as entrainer at 30 MPa and 50 degrees C in supercritical carbon dioxide (SC-CO2). It was found that entrainer increases the rate of extraction and yield substantially. SC-CO2+ethanol (4%) at 20MPa, 40 degrees C was investigated by HPLC/LC-ESI-MS for characterization of the xanthones. From liquid chromatography electron spray ionization mass spectrometry (LC-ESI-MS) spectra, 12 components were structurally correlated and confirmed based on the fragmentation characteristics and information available in the literature. The occurrence of these xanthone in SC-CO2 extract is reported for first time in G. mangostana species. The antioxidant activities of SC-CO2 were investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals (IC50 = 41.8 mu g/mL), lipid peroxidation (IC50 = 21.5 mu g/mL), hydroxyl radicals site specific (IC50 = 30.0 mu g/mL) and hydroxyl radicals non-site specific (IC50 = 23.1 mu g/mL). From cytochrome c assay it was observed that SC-CO2 extract can reduce ferric cytochrome c to ferrocytochrome c. The results showed that SC-CO2 had great potential as antioxidant agent. (C) 2009 Elsevier B.V. All rights reserved.