The dry and wet methods of preparation for composite inorganic solid electrolytes including styrene-butadiene copolymer (SBR) or silicone rubber (silicone) as polymer binder are investigated, and their electrochemical properties are analyzed. The SBR composite electrolytes prepared by the dry process showed higher conductivity than the one done by the wet process. For the composite electrolyte prepared by the wet process, the SBR coating on the electrolyte particles blocked lithium-ionic conduction. The electrolytes prepared by the dry process, on the other hand, showed the dispersion of SBR granular domains in the electrolyte matrix, which results in good contact between the electrolyte particles. However, by choosing an adequate polymer such as silicone rubber, the wet-processed composite shows a high Li ion-conductivity.