Amorphous solid electrolytes in the system Li2S-P2S3 were obtained in a narrow composition range at around 66.7 mol % Li2S content by a high-energy ball-milling process. The 66.7Li(2)S(.)33.3P(2)S(3) (mol %) sample showed the highest ion conductivity of 1.1 X 10(-4) S(.)cm(-1) at room temperature among the obtained samples. Cyclic voltammetry revealed that the sample had a wide electrochemical window of about 5 V.