Poly vinyl alcohol (PVA) and polyethylene glycol (PEG) blend based Mg2+ ion conducting polymer electrolytes have been prepared. Polyethylene glycol (PEG) with three different molecular weights 200,400 and 600 has been used and the effect of this molecular weight on the ionic onductivity of the electrolytes is studied through XRD, ac impedance technique. The analysis shows that the PEG with mol.wt 600 is more effective in reducing the crystallinity and enhancing the conductivity properties of the electrolytes.