Pd-Ni alloy nanocrystals, with a controlled Ni atom content ranging from 0 to 60%, were synthesized with a gas aggregation process. The mean size of the alloy nanoparticles was found to decrease with Ni content. Quantum conductance-based hydrogen sensors were fabricated by depositing films of closely spaced Pd-Ni nanoparticles in gas phase with a well-controlled coverage, on the surface of silicon chips prefabricated with interdigital electrodes. Significant changes on the alpha-beta phase transition behavior of PdHx and hence the hydrogen response characteristics of the nanoparticle-based sensors, induced by the incorporation of Ni into the Pd nanoparticles, were demonstrated. An optimal Ni content of 16% was suggested to make excellent H-2 sensors with rapid response, high sensitivity as well as good linearity and reliability in a wide hydrogen pressure range. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.