Composite polymer electrolytes based on polyethylene oxide (PEO), LiN(C2F5SO2)(2) (BETI), and BaTiO3 with particle size of 0.5 or 0.06 mum were prepared by hot press. Small amount of nanosize BaTiO3 powder (0.06 mum) into PEO12BETI polymer electrolyte results in enhanced conductivity while the addition of 0.5-mum powder as filler was found to enhance the transport number as well as conductivity. The combination of differential scanning calorimetry (DSC), impedance, spectroscopy (IS), and transmission electron microscope (TEM) measurements indicates that the addition of 0.06-mum filler chiefly influences PEO morphology while the addition of 0.5 mum predominantly increases salt dissociation.