Preliminary studies of gel electrolytes based on PMMA and solutions of the lithium salt LiN (CF3SO2)(2) in propylene carbonate (PC) and the mixed solvent propylene carbonate + ethylene carbonate (PC + EC) are presented. The influence of salt concentration on conductivity with different proportions of PMMA and different volume ratios of EC and PC has been investigated. Comparison of conductivity studies of the liquid electrolytes with the salts LiCF3SO3 and LiN(CF3SO2)(2) has also been made. The addition of PMMA to the liquid electrolytes increases the viscosity considerably without affecting their stable potential window resulting in thermally stable gels. The high conductivity attained by the gels (3 x 10(-3) S cm(-1)) at room temperature and their moderate variation with temperature made them very promising for electrochromic window applications