Nanosized alumina (Al2O3) was added to polyacrylonitrile (PAN)-lithium perchlorate (LiClO4) electrolytes. Infrared (IR) absorption spectroscopy was employed to study the influence of Al2O3 on the ionic association in the composite electrolyte. The nano-Al2O3 filler helped the dissolution of the salt and the dissociation of nitrile-Li+ interaction in the "dry" composite. Based on the Lewis acid-base type interactions of the surface groups on nano-Al2O3 particles with the ions and with the polymer and on the present and previous experimental results, an interpretation is proposed to the roles of the nanoscale ceramic particles on the enhancement of ionic conductivity and transference number of composite polymer electrolytes. (C) 2003 The Electrochemical Society.