In the present work, the effect of Li salt i.e. LiClO4 contained in composite plasticizer (PC+DEC) with three different concentrations on ionic transport and other electrochemical properties of PMMA based gel polymer electrolytes synthesized has been investigated. The electrolytes have been synthesized by solution casting technique by varying the wt (%) of salt and plasticizer. The formation of polymer-salt complexes and their structural characterization have been carried out by FTIR spectroscopic and XRD analyses. The room temperature ionic conductivity of the electrolyte composition 0.6PMMA-0.125(PC+DEC)-0.15LiClO4 (wt %) has been found to be maximum whose magnitude is 0.40×10-5 S/cm as determined by ac impedance analysis. The temperature dependent ionic conductivity of electrolyte sample0.6PMMA-0.125(PC+DEC)-0.15LiClO4 has further been investigated. Thermal analyses of electrolyte samples of all three compositions have also been done.