Electrodeposition of Mo alloys with iron group metals is of renewed interest. The electrodeposits are used as cathode materials in fuel cells. Electodeposition of Co-Mo alloy from triammonium citrate bath is described. To get a bright Co-Mo alloy deposit the optimum plating bath conditions are COSO4 0.3M, (NH4)(2)MoO4 0.25M, triammonium citrate 0.2M, pH 8, c.d 4A/dm(2) at 303K. Hardness of the alloy deposit increased with molybdenum content and annealing. Increase of Mo content in the alloy favoured electrocatalytic property for hydrogen evolution reaction. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.