The conductivity and viscosity behaviour of nano dispersed lithium ion-conducting polymer gel electrolytes containing solvents with different (low and high) dielectric constants have been studied. The conductivity of liquid electrolytes depends upon the dielectric constant of the solvent used and the addition of polymethylmethacrylate (PMMA) results in an increase in conductivity for electrolytes containing low dielectric constant solvent. This is an interesting behaviour observed for the first time in lithium ion-conducting polymer gel electrolytes where gels have higher conductivity than the corresponding liquid electrolytes which is due to the role of polymer in the dissociation of undissociated salt present in these electrolytes containing low dielectric constant solvent. The addition of nano size fumed silica to polymer gel electrolytes show different conductivity behaviour for electrolytes containing low and high dielectric constant solvent along with an increase in viscosity in each case. The nano dispersed gels so obtained show high conductivity similar to 10(-2) S/cm at 25 degrees C along with better mechanical properties. The conductivity does not show any appreciable change with time which is desirable for their use in devices. (c) 2005 Elsevier B.V. All rights reserved.