Hydrophilic fumed silica (SiO2)/polyacrylonitrile (PAN) composite electrolyte membranes were prepared by electrospinning composite solutions of SiO2 and PAN in N,N-dimethylformamide (DMF). Among electrospinning solutions with various SiO2 contents, the 12wt% SiO2 in PAN solution has highest zeta potential (−40.82mV), and exhibits the best dispersibility of SiO2 particles. The resultant 12wt% SiO2/PAN nanofiber membrane has the smallest average fiber diameter, highest porosity, and largest specific surface area. In addition, this membrane has a three-dimensional network structure, which is fully interconnected with combined mesopores and macropores because of a good SiO2 dispersion. Composite electrolyte membranes were prepared by soaking these porous nanofiber membranes in 1M lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1vol%). It is found that 12wt% SiO2/PAN electrolyte membrane has the highest conductivity (1.1×10−2 Scm−1) due to the large liquid electrolyte uptake (about 490%). In addition, the electrochemical performance of composite electrolyte membranes is also improved after the introduction of SiO2. For initial cycle, 12wt% SiO2/PAN composite electrolyte membrane delivers the discharge capacity of 139mAhg−1 as 98% of theoretical value, and still retains a high value of 127mAhg−1 as 89% at 150th cycle, which is significantly higher that of pure PAN nanofiber-based electrolyte membranes.