The liquid carbon dioxide (CO2) extraction of xanthones, such as α-mangostin from the pericarp of mangosteen (Garcinia mangostana Linn.), was enhanced using ultrasound at 5, 20 and 25 ºC. Mixtures of carbon dioxide and ethanol were used as solvents. The extraction pressure was from 8 to 14 MPa. To enhance the extraction yield, the solvent was irradiated with ultrasound. The yields of xanthones, such as α-mangostin, in the extraction were significantly improved without any change in the selectivity of the extract. We also qualitatively and quantitatively analyzed the xanthones in the extract using HPLC (high-performance liquid chromatography) as well as the extraction behavior. The effect of four operating parameters, temperature, pressure, ultrasound irradiation time and the composition of ethanol in the liquid CO2 solution, on the extraction yield was investigated using single-factor experiments. The improved ratio in yields of each xanthone between the ultrasonic-enhanced case and unenhanced case was calculated. The yields of xanthones in the extract were significantly improved by adjusting the operating temperature, ultrasound irradiation time and the composition of ethanol in the liquid CO2 solution, whereas no change in the selectivity of the extract was observed.