Wood was treated in hot compressed water at 200-350degreesC without a catalyst to produce charcoal. The charcoal carbonized at various temperatures under hot compressed water was mainly analyzed by FTIR in order to investigate the changes in the chemical structures during the carbonization process. The FT-IR spectra showed that the carbonization of wood was promoted by the increasing reaction temperature. The intensity of the peaks due to the -OH and -CH of wood became weak with the increasing reaction temperature. The dehydrogenation and deoxygenation in wood were observed during the treatment with the hot compressed water. The studies clarified that the carbonization of wood was promoted at low temperature using the hot compressed water.