A novel polymeric electrolyte system has been developed using oligo(ethylene oxide)-grafted polymethacrylate matrix and linear polyether which dissolves magnesium salts. Thermal analyses showed that the obtained polymeric electrolytes have homogeneous and amorphous phases over a wide temperature range. The ionic structure of the polymeric system was examined by Raman spectroscopy. The ionic conductance behavior of the polymeric electrolyte was investigated as solid Mg2+-ion conductors. The conductivity depended mostly on the kind of the dissolved magnesium salt. The highest conductivity was obtained for the polymeric electrolytes containing Mg[(CF3SO3)2N]2 (about 10−4 S cm−1 at room temperature). Addition of dimethyl formamide as a complex-forming liquid component in the polymeric electrolyte system enhanced the ionic conductivity. The dc polarization of an Mg/Mg cell using the polymeric electrolyte proved that Mg2+ is mobile in the present polymeric system.