Co-utilization of several sugars, especially xylose and glucose, is essential for economically feasible processes with high ethanol productivity. However, the majorproblem during xylose/glucose co-fermentation is that xylose is used very slowly until after glucose is completely consumed. Here, we demonstrated an effective co-fermentation process using xylose- and cellobiose-assimilating recombinant Saccharomyces cerevisiae. The recombinant yeast is able to consume xylose during xylose/cellobiose co-fermentation as rapidly as during glucose fermentation. After 72 h, 95.6% of xylose was consumed, despite the co-fermentation conditions, and the ethanol yield was 0.358 g-ethanol/g-total sugar. (C) 2008 Elsevier Inc. All rights reserved.