Polymer with trimethylene oxide (TMO) units prepared from ring-opening polymerization of an oxetane derivative is a candidate for the matrix of solid polymer electrolytes. We prepare an oxetane derivative with nitrile group, 3-(2-cyanoethoxymethyl)-3-ethyloxetane, CYAMEO. CYAMEO is polymerized by using a cationic initiator system. The structure of the resulted polymer, P(CYAMEO), is confirmed by NMR and FTIR spectroscopic techniques. Inorganic salts, such as lithium salts, can be dissolved in P(CYAMEO) matrix. FTIR and DSC results of P(CYAMEO)-based electrolyte films suggest that lithium ions in the P(CYAMEO) matrix interact with the nitrile side chains, mainly, and not with the oxygen atoms on the main chain of the P(CYAMEO). The conductivity at 30°C for P(CYAMEO)-based electrolyte films, P(CYAME)10(LiX)1, is 19.6μScm−1 (X=LiClO4), 6.59μScm−1 (BF4), 6.54μScm−1 (CF3SO3), and 25.0μScm−1 (N(CF3SO2)2). The rise in temperature from 30°C to 70°C increases their conductivity, about 30–40 times. The conductivity at 70°C for P(CYAMEO)-based electrolyte films is 0.742mScm−1 (X=LiClO4) and 0.703mScm−1 (N(CF3SO2)2). Electrochemical deposition and dissolution of lithium on a nickel plate electrode are observed in the solvent-free three-electrode electrochemical cell with P(CYAMEO)10(LiX)1, (X=ClO4 or N(CF3SO2)2) electrolyte film at 55°C.