The structure, crystallinity, thermal properties, kinetic analysis of thermal degradation and ionic conductivity of poly(ethylene oxide)/lithium montmorillonite (PEO/LiMMT) nanocomposites prepared by melt intercalation were investigated. An intercalated structure of PEO/LiMMT nanocomposites was found by small angle X-ray scattering (SAXS). Differential scanning calorimetry (DSC) shows that an addition of LiMMT decreases the crystallinity of PEO which completely disappears above 80wt.% of LiMMT and decreases PEO melting temperature. The influence of LiMMT on the PEO crystallinity was also observed by SAXS and Fourier Transform Infrared Spectroscopy (FTIR). Thermogravimetric analysis (TGA) indicates that LiMMT significantly lowers the thermal stability of PEO and changes its degradation mechanism what is confirmed by kinetic analysis using isoconversional method and deconvolution procedure. Electrochemical impedance spectroscopy reveals the significant increase in ionic conductivity at room temperature with addition of LiMMT and optimum LiMMT content concerning conductivity was defined.