Pt-M alloy nanoparticles (NPs) with well-defined size and compositions exhibit dramatically catalytic performance in chemical reactions. In this work, monodisperse PtCu NPs with controlled size and compositions were synthesized by the co-reduction method in the presence of oleylamine. These NPs have excellent catalytic activities in the hydrolytic dehydrogenation of ammonia borane (AB) and their activities were composition dependent. Among the different-composition PtCu NPs, the CusoPtso NPs exhibit the highest catalytic activity with an initial turnover frequency of 102.5 mol((hydrogen)) . mol((catalyst))(-1) . min(-1) and an apparent activation energy of 36 kJ.mol(-1), which demonstrate the validity of partly replacing Pt by a first-row transition metal on constructing high performance heterogeneous nanocatalysts for the hydrolytic dehydrogenation of AB. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.