Amorphous solid electrolytes in the Li2S-P2S5 system were prepared successfully from a mixture of crystalline Li2S and P2S5, using a mechanical milling technique. The amorphous-forming region,vas extended to higher Li2S compositions by mechanical milling, compared with melt quenching. The pelletized samples of the 75Li(2)S . 25P(2)S(5) (on a mole-percent basis) amorphous powders obtained by mechanical milling for 20 h exhibited high conductivity (2 x 10(-4) S/cm at room temperature) and an activation energy for conduction of 34 kJ/mol. The lithium-ion transport number of the amorphous powders was almost unity.