Producing hydrogen through aqueous phase reforming (APR) of low-boiling fraction (LBF) which is obtained by distilling the crude bio-oil at reduced pressure is a promising way to categorize it as resource rather than waste. The catalytic conversion of renewable sources using catalyst with the best reactivity is essential to make the most of energy. The size effect of catalyst on APR of LBF has been studied. A series of gamma-Al2O3 supported Pt nano-particles catalysts with average sizes ranging from 1.6 nm to 5.7 nm were synthesized. The activity of this reaction and selectivity to hydrogen increased as the Pt particle size decreased. The full-shell cuboctahedron model was used to explain the phenomenon. It was proposed that the reaction activity and selectivity were size sensitive. Because particles with different size had different constitution of atoms and atoms at edges were the active sites for APR of LBF. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.