We report the electrodeposition of Cu and Ni in aqueous solutions together with the deposition of lanthanides (Gd, Sm, Dy, Tb) and amorphous magnetic alloys of lanthanides with transition metals (Fe, Co) onto various polymer cathodes in formamide solutions. We used conducting polymers (polypyrrole, PPy; polyethylenedioxythiophene, PEDOT) sprayed on different substrates and in addition composite materials based on carbon black (CB) mixed either with polyethylene (PE) or with polycarbonate (PC). In the latter case, the conducting material is easily shaped out in various forms. When deposited on some of these substrates, the alloys appear as an interesting material for magneto-optic recording. The electrochemical process was used for the preparation of Gd/Co and Dy/Fe alloys for which the measured coercitive fields ranged from 250–300 Oe (Dy/Fe) to about 350 Oe (Gd/Fe). We demonstrated also the feasibility of an additional electrografting of a transparent protective layer of polyacrylonitrile (PAN) in order to avoid the corrosion of the alloys by the atmosphere.