Antioxidant compounds from mangosteen pericarps have been extracted with low-transition-temperature mixture (LTTM) assisted hydrothermal method. Extracted antioxidant compounds were determined as xanthone and total phenolic compounds. The effects of temperature, concentration of LTTM, and sonication pretreatment on the recovery of xanthone and total phenolic compounds were investigated. Extraction were carried out in a batch extractor at various temperatures (120 - 160°C), concentrations of LTTM (0.1 - 0.3 mg/mL), and sonication pretreatments (0 - 10 min). LTTM used for extraction was consisted of citric acid as hydrogen bond donor and alanine as hydrogen bond acceptor. Xanthone and total phenolic compounds were analyzed by spectrophotometer. In order to determine the effect of extraction condition on the antioxidant efficiency of the extract, the antioxidant efficiency of extract were analyzed by DPPH assay method. Based on the result, the recovery of xanthone increased as increasing temperature and concentration of LTTM. Inversely, the recovery of total phenolic compounds decreased as increasing temperature. The sonication pretreatment had significantly effect on the recovery of both xanthone and total phenolic compounds, however the optimum condition of sonication pretreatment was at 5 min. The antioxidant efficiency of the extract was affected by the extraction condition, and the highest antioxidant efficiency was 1.395 obtained at temperature of 120°C, LTTM concentration of 0.3 mg/mL, and sonication time of 5 min.