The Mo-Ni-O powders were electrodeposited from ammonium sulfate containing electrolytes with different Mo/Ni ion concentration ratios. The phase composition of these powders was investigated using TEM. EDS and XRD analysis. The TEM analysis showed that two types of particles were present in the powders: amorphous and crystalline. For crystalline particles it was found that two phases, MoO3 and MoNi4 prevail in all powders, while the NiO phase was detected in the powder electrodeposited at Mo/Ni = 0.3/1. These findings are in good agreement with our previous results where MoO3, MoNi4 and NiMoO4 phases were detected in the recrystallized Mo-Ni-O powders. In this work we discovered that the NiMoO4 phase was formed by solid state reaction between NiO and MoO3 at elevated temperature. (C) 2010 Elsevier Ltd. All rights reserved.