Poly(ethylene oxide) PEO/Na--montmorillonite and polyethylene-poly(ethylene glycol) (PE-PEG) diblock copolymer/Na+-montmorillonite nanocomposites have been prepared by melt intercalation method. The effect of thermal treatment on the amount of PEO and PE-PEG diblock copolymer intercalated into layers of Na+-montmorillonite and on ionic conductivity of PEO/Na+-MMT nanocomposites have been evaluated. It was found that PEO can be intercalated into the layers of Na+-MMT by simple mechanical blending and part of PE in PE-PEG diblock copolymers was also intercalated into the layers of Na--MMT. The intercalated amount increases with thermal treatment time, which improves the ionic conductivity of the PEO/Na-divided by-MMT nanocomposites. PE-PEG diblock copolymer/Na+-MMT hybrids can be considered as a new kind of fillers for the reinforcement of polyethylene. By only adding a small amount (1 - 15% by weight) of these fillers, tensile strength of polyethylene was improved significantly. This research provides valuable information for the development of new kinds of fillers for polymer reinforcement, and polyelectrolytes.