Preparation and characterization of hot-pressed Li+ ion conducting Polyethylene oxide (PEO) composite electrolytes are discussed in this paper. Lithium trifluoromethanesulfonate with linear formula CF3SO3Li is selected as Li+ ion source for polymer composite electrolyte processing. Polyethylene oxide as matrix for polymer electrolyte is selected, because of its cation solvatation and salt complexes formation partibility. Nano-sized fillers such as carbon nanotube (CNT) and graphene (GR) are introduced to polymeric composite to improve PEO electrolyte mechanical properties. The composites were prepared from PEO, CF3SO3Li, CNT and GR by solution casting and by hot-pressing method. Influence of CF3SO3Li, CNT and GR concentrations on the electrical, thermal and mechanical properties of PEO composite is investigated and discussed.