Preparation of catalysts with high catalytic activity toward hydrogen generation from ammonia borane (AB) hydrolysis is of significant importance because of the important and versatile applications of hydrogen. Herein we report the synthesis of Ru nanoparticles supported on nanodiamond by a one-step approach through the reduction of RuCl3 using AB as reducing agent. The nanocomposites surfaces with large quantity of oxygen containing functional groups such as hydroxyl and carboxylic groups resulted in a homogeneous suspension in aqueous phase. The catalytic activity of Ru/nanodiamond was studied for hydrogen generation from AB hydrolysis at 25 degrees C. Results indicated that nanodiamond supported Ru nanoparticles with a mean particle size of 3.7 nm exhibited high catalytic activity for AB hydrolysis, with a turnover frequency number of 229 mol H-2 center dot(mol Ru center dot min)(-1). The high catalytic activity of Ru/nanodiamond demonstrates that nano diamond is a good media for nanoparticles immobilization. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.