This thesis investigates the impact of the addition of lithium montmorillonite (Li-MMT) on thermal transitions (glass transition temperature, melting temperature), crystallinity and ion conductivity of poly(ethylene oxide) (PEO) and poly(ethylene glycol) (PEG). Methods used in the study were differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and electrochemical impedance spectroscopy (EIS). Li-MMT was prepared by ion exchange process from natural montmorillonite, while samples of PEO/Li- MMT and PEG/LiMMT are prepared by melt intercalation method. Samples that were studied had weight ratios of PEO/Li-MMT: 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80, 10/90 and PEG/Li-MMT: 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80, 10/90. Differential scanning calorimetry was used to determine the influence of Li-MMT on thermal transitions (glass transition temperature, melting temperature) and the crystallinity of PEO and PEG polymers. It was determined that the addition of Li-MMT decreasedtheir glass transition temperature, the melting temperatureand the crystallinity. Influence of Li-MMT on the structure of PEO and PEG was examined by infrared spectroscopy. The results show that the addition of Li-MMT distortsthe helical conformation of PEO and PEG macromolecules. The helical conformation is the necessary condition for the crystallinity of these polymers. Influence of the addition of Li-MMT on the ionic conductivity of PEO and PEG was examined by electrochemical impedance spectroscopy. It was determined that by addition of the Li-MMT ionic conductivity of PEO increases and the optimum addition of Li-MMT was defined. The addition of Li- MMT does not positively influence ionic conductivity of PEG.