The electrical and electrochemical properties of the Li2S–P2S5–P2O5 glass–ceramic electrolytes were investigated. The 80Li2S·(20− x)P2S5·xP2O5 (mol%) glass–ceramics were prepared by a mechanical milling and a subsequent heat treatment. The 80Li2S·19P2S5·1P2O5 glass–ceramic showed the high lithium ion conductivity of 7.4×10−4 Scm−1 at room temperature and the low activation energy of 34kJmol−1 for conduction. The addition of a small amount of P2O5 to the Li2S–P2S5 sulfide system lowered the electronic conductivity and enhanced the electrochemical stability of the glass–ceramic electrolytes. All-solid-state In/LiCoO2 cells with the 80Li2S·19P2S5·1P2O5 glass–ceramic as a solid electrolyte worked as lithium secondary batteries at room temperature. The cells maintained high discharge capacity of about 100mAhg−1 for 10 cycles.