The microscopic size effect of microhardness that we have found earlier for electrodeposited binary alloys of tungsten and the iron group metals is explained here by an increased concentration of oxygen-containing impurities in the coatings, revealed for Co-W alloys. An increase in oxygen-containing impurities correlates with the volume current density (VCD), meaning that microhardness of electrodeposited alloys diminishes at a higher VCD. The properties of the coatings (e.g., microhardness) are also affected by the nature of the anode used, since the complex from which electrodeposition of the alloys occurs and which contains a metal ion from the iron group metals is consumed not only at the cathode, but is subject to oxidation at the anode as well.