Li₂S-P₂S₅-based glass-ceramics were prepared by mechanical milling and subsequent heat-treatment. In the systems Li₂S-P₂S₅-GeS₂ and Li₂S-P₂S₅-SiS₂, the conductivities increased with an increase in the heat-treatment temperature and exhibited high values over 10^-3 S•cm^-1 after heating at 550 oC. The high conductivities were mainly caused by the formation of superionic crystals analogous to thio-LISICON in the Li₃PS₄-Li₄GeS₄ solid solutions. All-solid-state cells such as In-Li / Li_4/3Ti_5/3O₄ using the highly conductive glass-ceramic electrolytes worked at room temperature and maintained high charge-discharge capacities of over 100 mAh•g^-1 even at the 300th cycle.