The immobilization of copolymers of hydrophilic N-vinyl-pyrrolidone and polymerizable derivatives of the transition metal complex (pentamethylcyclopentadienyl-2,2’-bipyridine chloro) rhodium(III) ([Rh-III(C(5)Me(5))(bpy)Cl](+)) by gamma-irradiation on an electrode surface to obtain swellable and highly permeable redox active polymer films which swell easily is described. These polymer films swell easily in water and thus provide a three-dimensional reaction layer, which should be advantageous for electrocatalytic processes mediated by the surface-confined rhodium complex. Rotating disk voltammetry is used to investigate the influence of radiation dose and the amount of immobilized polymer on the permeability of the polymer films. Furthermore, cyclic voltammograms show that the rhodium complex retains its electrochemical activity and also its ability to mediate the electrochemical reduction of the cofactor nicotinamide adenine dinucleotide (NAD(+)).