Carbon nanotube (CNT)-supported ruthenium catalysts were studied for the hydrogenation of cellobiose in neutral water medium. The acidity of catalysts and the size of Ru particles played key roles in the conversion of cellobiose to sorbitol. A higher concentration of nitric acid used for CNT pretreatment provided a better sorbitol yield, suggesting an important role of catalyst acidity. The catalysts with larger mean sizes of Ru particles and abundant acidic sites exhibited better sorbitol yields, while those with smaller Ru particles and less acidic sites favored the formation of 3-beta-D-glucopyranosyl-D-glucitol. We elucidated that cellobiose was first converted to 3-beta-D-glucopyranosyl-D-glucitol via the hydrogenolysis, and then sorbitol was formed through the cleavage of beta-1,4-glycosidic bond in 3-beta-D-glucopyranosyl-D-glucitol over the catalysts. The catalyst with smaller Ru particles favored the first step but was disadvantageous to the second step due to the less acidity. Smaller Ru particles also accelerated the degradation of sorbitol. (C) 2010 Elsevier Inc. All rights reserved.