To identify the hydrolysis characteristics of cellulose, the main component of biomass, the decomposition rate and yield for conversion from cellulose into products were compared by varying reaction temperature, pressure and time in the range of the subcritical and supercritical water. A series of experiments were conducted to feed cellulose slurry continuously in the ranges of temperature 330-400 ℃, pressure 25-40 MPa and residence time 0.016-3.5 sec with a high pressure slurry pump. The decomposition rate of cellulose increased linearly with increasing temperature without a pressure effect in the subcritical region. Meanwhile, in the case of 40 MPa at the supercritical region, the rate constant increased almost linearly like in the subcritical region but the decomposition rate at the pressure of 25 MPa increased drastically more than that of the subcritical water due to the extreme decrease in density(gas-like phase; ρ≒0.17). It was shown that yields of hydrolysis products increased with increasing pressure at each temperature. However, as the residence time increases, yields of hydrolysis products decreased and those of pyrolysis products increased. The maximum yields of hydrolysis products and glucose were 90.20 wt% and 39.68 wt% at 330 ℃ in the subcritical region, 92.39 wt% and 35.19 wt% at 360 ℃ in the near-critical region and 82.61 wt% the 21.20 wt% at 400 o C in the supercritical region. Consequently, although the decomposition rate of cellulose jumped up at 25 MPa in the supercritical region, yields of hydrolysis products and glucose were much higher in the subcritical region than those in the supercritical region, considering the selectivity.