To clarify the thermal-softening properties of water-swollen wood, the viscoelastic properties of wood specimens conditioned to various moisture contents and of water solutions of amorphous cellulose, hemicellulose and milled wood lignin, have been studied in the temperature range from -150 to 0 degreesC at frequencies ranging between 0.5 and 10 Hz. A relaxation process around -40 degreesC was observed in wood specimen with high moisture content. It was observed in wood specimens with lower moisture content at higher temperature. The value of apparent activation energy for the relaxation process was 50 kJ/mol. On the other hand, a similar relaxation process was observed in water solutions of amorphous cellulose and hemicellulose around -40 degreesC, but it was not observed in water or water solution of milled wood lignin. The values of apparent activation energy for the relaxation process were 230-545 kJ/mol. Therefore, we considered that the relaxation process was due to the water-swollen polysaccharides and affected by the situations of water molecules.