Polymer electrolytes based on phosphate-polyether networks (PPNs) were synthesized by polycondensation reaction of phosphorus oxychloride (POCl3) with PEG/PTMG (70/30) copolymers to improve ionic conductivity at ambient temperatures. Ion conductivity and thermal behavior of PPN series-LiCF3SO3 complexes were investigated with various salt concentration, temperatures and plasticizer contents. Ethylene carbonate (EC) as a plasticizer was added to a phosphate-polyether network to improve ionic conductivity at room temperature. The PPN1000/LiCF3SO3/EC electrolyte exhibited ionic conductivity of 1.01 x 10(-4) S cm(-1) at 25 degrees C. PPN1000-LiCF3SO3 complexes showed a higher ionic conductivity than PPN600-LiCF3SO3 complexes due to the solvating ability of network polymer electrolytes. The network structure of PPN series-LiCF3SO3 complexes caused a considerable decrease in the degree of crystallinity, resulting in a high ionic conductivity.