In this research poplar wood meals were treated with supercritical water for 60s in the temperature range between 325°C and 425°C at the fixed pressure at 220±10atm in order to develop effective saccharification process of lignocellulosics and to analyze chemical feature of solid residues produced from the process. The solid residues obtained from degradation products by filtration were consisted of chemically modified lignin and fibrous materials. Glucose and xylose were identified as main sugar components of fibrous materials, and the highest ratio of glucose/xylose in fibrous materials was achieved at the highest reaction temperature. At the reaction temperature of 425°C the more than 80% of solid residues was composed of lignin. The molecular weight of lignin in solid residues was ranged between 4,000 and 1,500 by GPC analysis, which is only 1/4 to 1/9 folds compared to that of milled wood lignin (MWL) isolated from poplar wood determined to ca. 13,500. This result suggested that lignin was severely fragmented to almost oligo-state molecular weight level. Assuming that average molecular weight of monomeric units of lignin (coniferyl and sinapyl alcohol) could be 200, the lignin is solid residues could be constructed only with 12 to 15 monomeric units. In addition, DFRC analysis suggested that β-O-4 linkage was not detected in the lignin in solid residues, indicating that two major reactions, cleavage of β-O-4 linkage as well as propane side chains, could occur under the condition of high temperature and pressure. Those structural features of lignins were clearly confirmed by ¹H and ¹³C NMR spectroscopic analysis.