Twenty natural plants from Jeju were extracted by pressurized organic solvent (100% methanol, 40 o C, 13.6 MPa, 10 min). Extraction yield, total phenolic content (TPC) and integral antioxidant capacity were measured, and each component was identified by GC/MS. Extraction yields were high as 21. 8%, 21.5, 21.1, 20.7 and 20.1% in Rhus javanica, Euscaphis japonica, Alnus firma, Sapium japonicum and Sorbus alnifolia, respectively. The extracts containing high TPC (mg GAE/g of dry sample) were obtained from Malus sieboldii (68.3), Sapium japonicum (57.6), Pyrrosia lingua (56.6) and Euscaphis japonica (55.1). Integral antioxidant capacities of water-soluble substances were 598, 394, 293 and 270 μmol ascorbic acid equivalent/g in Geranium thunbergii, Sapium japonicum, Cornus kousa and Rhus javanica, respectively. Integral antioxidant capacities of lipidsoluble substances were 611, 314, 296 and 242 μmol trolox equivalent/g in Ardisia crenata, Ostrya japonica, Geranium thunbergii and Quercus acuta, respectively. Fifteen major peaks were identified by GC/MS from the extract of pressurized organic solvent from Sapium japonicum. Two polyphenols (gallic acid (retention time (RT) 19.7 min)) and quercetin (33.5 min)), ascorbic acid (RT 35.3 min), and several fatty acids (retention time 18.6, 21.0, 21.8, 21.9 and 23.6 min) were identified, and gallic acid was the major polyphenol component due to high peak area.