Rice straw has attracted significant interest in Japan as a potential raw material for biorefineries. Combination of hot-compressed water treatment (HCWT) and wet disk milling (WDM) was investigated to improve the enzymatic digestibility of rice straw and enhance sugar recovery yield. Rice straw, cut to <3 mm, was autoclaved at 121, 135, and 150 degrees C for 60 min, and subsequently treated by wet disk milling. WDM with HCWT at 135 degrees C for 60 min produced maximum xylose and glucose yields of 79% and 90%. respectively, at 10 FPU/g-substrate cellulase loading. Autoclaving at 150 degrees C leaked a 35% arabinose effluence in the liquid phase. Hydrolysis via WDM with HCWT required a lower enzyme loading (5 FPU/g-substrate) than either pretreatment process in isolation for >70% xylose and 80% glucose yield. Economical analysis indicate that enzymes cost for ethanol production is reduced by 19-67% by WDM with HCWT. (C) 2011 Elsevier Ltd. All rights reserved.