Cellulose was hydrolyzed with hot-compressed water (HCW; similar to310 degreesC, 9.8 Mpa) using an HCW-flow reactor. HCW was continuously delivered into a reactor charged with cellulose. The effluent from the reactor was cooled and separated into a water-soluble fraction (WS) and a water-insoluble fraction which deposited after cooling (DP). Cellulose started to decompose into WS and DP when HCW was delivered above 230 degreesC. The main components of the WS were hexose and oligosaccharides ranging from a dimer to a pentamer, and the DP consisted of polysaccharides ranging from a hexamer to an eicosamer or more polymerized saccharides. When HCW was delivered at 295 degreesC, nearly all of the cellulose decomposed after a 12-min flow of HCW, and 81 wt % of WS and 18 wt % of DP were obtained. The formation rates of WS and DP increased as the temperature of HCW increased. However, the composition of WS and DP barely changed with the HCW temperature under around 280 degreesC, which corresponds to the softening point of the cellulose. When the HCW temperature was further increased, the depolymerization of the products proceeded. The decomposition rate of cellulose itself was not affected by the flow rate of HCW, but the depolymerization of the products was suppressed when the flow rate of the HCW was increased.