The electrochemical formation processes of holmium-cobalt alloys on cobalt cathode in molten HoC13-KC1 wereinvestigated by cyclic voltammetry and open current potential-time curve after potentiostatic electrolysis. The structure ofHo-Co alloys films deposited on cobalt electrode by potentiostatic electrolysis was characterized by X-ray diffraction. Thestandard Gibbs free energies of formation for the intermetallic compounds of Ho and Co were determined. The diffusioncoefficient and diffusion activation energy of Ho atom in the alloy phase were calculated to be 10-10-10-11 cm2/s and 96.0kJ/mol, respectively, from the current-time curve at potential step.