The optimal pH value of the concentrated boron–gluconate bath for electroplating Co–W coatings is established to be 6.5 (the concentrations of the alloying components are raised by a factor of 5 compared with the commonly used electrolyte). The microhardness of binary Co–W alloys obtained from this bath reaches 1000 kg mm^–2, and electrodeposition proceeds with high current efficiency (93–95%). We demonstrate the critical role the volume current density plays in determining the microhardness of the binary coatings electrodeposited from this bath under galvanostatic conditions. We attribute this peculiarity of the investigated system to microhardness size effect, which is associated with structural modifications in the plated coatings that can be induced by changing the volume current density. Using the concentrated bath improves efficiency of electrodeposition.