The electrochemical, theological, calorimetric, spectroscopic and morphological investigations have been used to examine poly(methyl methacrylate), PMMA based electrolytes dispersed with nano-sized fumed silica (SiO2). The observed ionic conductivity was one of the highest and is of the order similar to mS/cm at ambient temperature which was studied as a function of concentration of fumed silica nano-particles. It was further found that the fumed silica acted as a passive filler and played a predominant role in controlling the theological properties while ion transport properties were least effected. The differential calorimetry studies revealed single glass transition temperature pointing towards homogeneous nature of the composite polymeric electrolytes (CPEs). At an optimum concentration of fumed silica (2 wt%) the observed maximum conductivity and morphology was attributed to the presence of a strong network structure, while at a higher concentration the elastic behavior was more pronounced which impeded ion transport. This contention was supported by spectroscopic data. (c) 2006 Published by Elsevier Ltd.