Sodium 2-[omega-methacryloyl oligo(oxyethylene)] ethylsulfonate has been synthesized and polymerized to prepare a polymeric solid electrolyte with Na+ single-ionic conductivity. The length of oligo(oxyethylene) side chain determines the glass transition temperature and salt concentration of the homopolymers, and consequently influences the conductivity. The highest conductivity of 3.5 x 10(-6) S cm-1 at 25-degrees-C is obtained when the number of CH2CH2O repeat units in the side chain is equal to 14. The temperature dependence of the ionic conductivity shows a curved Arrhenius plot, suggesting that ionic conduction is closely associated with segmental motion of the polymer host. The Williams-Landel-Ferry (WLF) empirical equation, which is based on the free-volume theory, is found to be valid for describing the conductivity data, and the obtained WLF parameters are comparable with the universal values.