Polymeric electrolytes consisting of oligo(ethylene oxide)-grafted poly(methylmethacrylate), organic plasticizer and inorganic salts of multivalent cations (Mg2+, La3+, Ce3+ and Yb3+) have been prepared. Their behavior as solid ion conductors has been examined. Thermal and X-ray analyses showed that the polymeric electrolytes were homogeneous and amorphous over a wide temperature range. Ionic conductivities of 10−4 and 10−5 S cm−1 were obtained at room temperature for the polymeric films containing Mg(ClO4)2 and Ce(ClO4)3, respectively. The ionic conductivity depends critically on the composition of the polymer electrolytes. The ionic coordination in the polymeric electrolytes, as determined by Raman spectroscopy, is discussed in relation to the conductance behavior.