The importance of the passivation layer on Fe powder surfaces formed by oxides, hydroxides, and/or salts and water molecules is pointed out for both electrochemical oxidative dissolution of iron powder and electrodeposition of Ni layer on it. This layer behaves as ohmic contact resistance. The layer thickness affects the surface reactivity of the powder and is influenced by the way of preactivation the powder prior to the electrochemical process. A reliable voltammetric method reflecting the surface reactivity was found, theoretically treated, and experimentally verified by measuring the rate of electrochemical dissolution of Fe powder. The efficiency of Ni electrodeposition on this powder was determined in a series of independent electrolyses. The correlation between both later mentioned parameters was satisfying for small powder particle fractions as well as for activation procedures which include chemical step.