Both nonelectrically deposited Co‐P and Co‐Fe‐B and electrically deposited Co films were prepared on rapid‐quenched amorphous alloy ribbons. These Co‐based alloy deposits exhibited characteristic polycrystalline structures, surface morphology, and magnetic properties, which were dependent on the species of the amorphous substrates. The electrochemical polarization measurements of substrate electrodes revealed that the electrocatalysis of substrates (e.g., for the anodic oxidation of reducing agent) thoroughly interpreted the deposition potential and the rate of nonelectrical deposition, and the overpotential of electrical deposition were dependent on alloy element of substrate. These electrochemical parameters influence the initial step of deposition, and hence determine the structural and magnetic properties of the deposits obtained. Furthermore, a basic study of the electrical deposition processes on an amorphous ribbon substrate has been carried out in connection with the structural and magnetic properties of the deposits. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 17–25, 2000