The semi-pilot scale of continuous flow type hydrothermal reactor has been investigated to separate hemicellulose fraction from corncob. We obtained the effective recovery of hemicellulose using tubular type reactor at 200 degrees C for 10 min. From constituent sugar analysis of corncob, 82.2% of xylan fraction was recovered as mixture of xylose, xylooligosaccharides and higher-xylooligosaccharide which has more than DIP 10. During purification of solubilized fraction by hydrothermal reaction such as ultrafiltration and ion exchange resin, higher-xylooligosaccharide was recovered as the precipitate. This precipitate was identified as non-blanched xylan fraction which has from DIP 11 to DP 21 mainly. In this system, only a small amount of furfural has been generated. This tubular reactor has a characteristic controllability of thermal history, and seems to be effective for sugar recovery from soft biomass like corncob. (c) 2008 Elsevier Ltd. All rights reserved.