This aper investigates the influence of the addition of organically modified montmorillonite Cloisite 93A on thermal transitions (glass transition temperature, melting and crystallization temperature), crystallinity, thermal stability and structure of poly (ethylene oxide) of average molecular mass M v ̅̅̅̅ = 1 000 000 (PEO10) in PEO10/Cloisite 93A nanocomposites and its influence on the ionic conductivity of PEO10 in PEO10/Cloisite 93A/LiBOB nanocomposite polymer electrolytes. Polymer nanocomposites were prepared in two series. In the first one, PEO10/Cloisite 93A nanocomposites with different weight ratios (100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80, 10/90, 0/100) were prepared by the melt intercalation method. In the second one, PEO10/Cloisite 93A/LiBOB nanocomposites with different polymers and fillers weight ratios (100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80, 10/90, 0/100) were also prepared by melt intercalation method. Lithium salt (LiBOB) was added to provide a Li + ion conducting electrolyte with enough concentration of charge carriers in an amount that achives mole ratio of lithium cation: ether-oxygen = 1:8. Differential scanning calorimetry (DSC) analysis indicates that the addition of filler reduces melting and crystallization temperatures of PEO, but does not significantly affect its glass transition temperatures. The addition of the filler reduces the melting and crystallization enthalpy of poly (ethylene oxide), suggesting a reduction of its degree of crystallinity. Thermogravimetric analysis (TGA) shows that the addition of filler reduces thermal stability of poly (ethylene oxide). Fourier Transformation Infrared Spectroscopy (FT-IR) observes that the addition of the filler causes distortion of the spiral conformation of the poly (ethylene oxide), which indicates a change in its crystallinity. Electrochemical impedance spectroscopy (EIS) shows that the ionic conductivity of the PEO10/Cloisite 93A/LiBOB nanocomposites increases by adding the filler to a certain optimum value after which it starts to decrease. This indicates that the conductivity, besides the degree of crystallinity, is also influenced by the dispersion of fillers in the matrix.