Via a two-step phase inversion technique, composite membranes with controllable porosity and a significant improvement of electrochemical properties were successfully prepared. The presence of surface functionalized mesoporous silica (SS) as inorganic fillers in the sulfonated polyethersulfone (sPES) polymer matrix was proved to have a great impact on the resultant membrane structure, which subsequently led to significantly enhanced ionic conductivity of the membranes. The correlation among inorganic fillers, composite structures, electrochemical properties and desalination performance by electrodialysis (ED) was discussed in detail. The optimal membrane was the composite with 0.2 wt% SS loading, which possessed a good ionic conductivity of 5.554 mS cm-1, a high selectivity with 0.95 transport number while maintaining good mechanical strength and thermal stability. Moreover, the performance of this membrane in ED was comparable to a commercial membrane (FKE), exhibiting a current efficiency of 0.84 and 3.82 kW h kg-1 of salt removed. © 2011 The Royal Society of Chemistry.