An extrusion process involving a twin-screw extruder was used for the micro/nanofibrillation of Douglas fir and Eucalyptus treated with hot-compressed water (HCW). Partial removal of hemicellulose and lignin by HCW treatment effectively improved the fibrillation by extrusion. Only HCW treatment produced glucose less than 5 weight percent (wt.%) in Douglas fir in a temperature range of 140-180 degrees C by enzymatic hydrolysis. Glucose production yields of 18 and 26 wt.% were obtained by HCW treatment at 170 and 180 degrees C, respectively, in Eucalyptus. Use of extrusion after HCW treatment drastically improved monosaccharide production yield in both woods. In the case of Douglas fir, the obtained values were 5 times higher than those obtained by HCW treatment alone. Total monosaccharide production yields were higher in Eucalyptus than in Douglas fir. The extruded production had a fine fibrous morphology on a sub-micro/nanoscopic scale. This result shows the great potential of the extrusion process after HCW treatment as a cost-effective pretreatment for enzymatic saccharification of woody biomass. (C) 2010 Elsevier Ltd. All rights reserved.