Electroless plating of copper and nickel via a one-step, tin-free activation process was carried out effectively on polyimide (PI, Kapton(R) FIN) films modified by UV induced surface graft copolymerization with 1-vinylimidazole (VIDz). The UV-induced surface graft copolymerization of VIDz was carried out on the Ar plasma-pretreated PI films via a solvent-free process under the atmospheric condition. Differing from the conventional "two-step" activation method for electroless plating, the one-step, Sn-free process. involved the direct activation of the graft-modified PI films in a PdCl2 or a Pd(NO3)(2) solution without prior sensitization by SnCl2. X-ray photoelectron spectroscopy (XPS) results showed that the VIDz-graft-copolymerized PI surface (the VIDz-g-PI surface) was much more susceptible to the electroless deposition of metals via the Sn-free process than the PI surfaces modified by Ar plasma treatment, N-2 plasma treatment, or chemical treatment. A T-peel adhesion strength of about 9 N/cm was achieved for the electrolessly deposited Ni and Cu on the VIDz-g-PI surfaces (the Ni/VIDZ-g-PI and the Cu/VIDz-g-PI assemblies). The high adhesion strength of the metal/VIDz-g-PI assemblies was attributed to the synergistic effect of strong spatial interactions of the grafted VIDz polymer chains with the metal atoms (including the Pd atoms), and the fact that the VIDz polymer chains were covalently tethered on the PI surface. XPS results also revealed that the metal/VIDz-g-PI assemblies delaminated by cohesive failure inside the PI film.