Composite polymer electrolytes based on poly(ethylene oxide) (PEO) were prepared by using LiClO4 as doping salts and silane-modified SiO2 as filler. Electrochemical, thermal and mechanical properties of PEO-based polymer electrolytes mixed with modified SiO2 were studied. Differential scanning calorimetry (DSC) results showed that in the presence of the filler, there is a decrease in the glass transition temperature of the electrolyte, whereas, on the other hand, enhances the crystallinity of the sample. Compared with unmodified SiO2 as inert filler, the addition of silane-modified SiO2 increases the ionic conductivity of the (PEO)16LiClO4 more noticeably, and leads to remarkable enhancement in the mechanical properties of polymer electrolytes.