In the present work, using nanosized rare earth oxide CeO2 as filler and acetonitrile as organic solvent, a novel solid-state composite polymer electrolyte (CPE) films (PEO)10LiClO4-x wt.%CeO2 (x=0,2,6,9,12,15) was prepared by solution-casting technique. The effect of CeO2 filler concentration on morphology and electrical characteristics of CPE films has been investigated and analyzed. The AC impedance measurements show that the ionic conductivity of CPE can be efficiently enhanced by adding appropriate CeO2. The highest room temperature (25OC) ionic conductivity of 1.71×10-5S•cm-1 is achieved with the CeO2 content of 9 wt.%. With the CeO2 content continues to increase, CPE ionic conductivity begin to decline. This is because appropriate CeO2 can disorder the chain structure and effectively inhibit the crystallization of PEO, which expands the amorphous region required for the lithium-ion transport.