The extraction of xanthones, such as α-mangostin from the pericarp of mangosteen (Garcinia mangostana Linn.) by supercritical fluid extraction (SFE), for which the solvent was carbon dioxide (CO2), was carried out at 35, 40 and 50 ºC. The extraction pressure was from 10 to 20 MPa. In order to enhance the yield of the extraction, ethanol was added as an entrainer. The yields of xanthones, such as α-mangostin in the extraction were significantly improved, whereas a change in the selectivity of the extract was not observed. We also conducted qualitative and quantitative analyses for xanthones in the extract by HPLC, and analyzed the extraction behavior. The effect of three operating parameters, such as temperature, pressure and the mole fraction of ethanol in a supercritical solution of CO2 on the extraction yield was investigated using the single-factor method.