The influence of water on asymmetric hydrogenation of alpha-ketoesters on platinum nanoparticles confined in the channels of carbon nanotubes was investigated. As high as 95% enantioselectivity is achieved in the asymmetric hydrogenation of ethyl pyruvate in acetic acid/water solution compared with 86% enantioselectivity obtained in anhydrous acetic acid. The adsorption experiment confirmed that the presence of water can enrich the chiral modifier cinchonidine in the channels 3900 times of that in solution and also enhance the ability of the channels to discriminate between the reactant and product molecules with only small hydrophobic/hydrophilic difference that kinetically favors the catalytic reaction in the channels of carbon nanotubes. (C) 2013 Published by Elsevier Inc.