The amorphous and crystalline 75Li(2)S center dot(25-x)P2S5 center dot xP(2)Se(5) solid electrolytes were prepared by simple mechanical milling method and heat-treatment. The structural analysis shows that selenium is effectively incorporated into the amorphous matrix and crystal lattice by mechanical milling, which results in the formation of the Se incorporated network units. In addition, the high lithium ion conducting phase similar to thio-LISICON III phase was precipitated at whole composition range after heat-treatment. For both amorphous and crystalline electrolytes, the ionic conductivities were enhanced with an increase of Se contents, and the crystalline electrolyte with 2 mol% of P2Se5 showed the highest conductivity of 6 x 10(-4)S cm(-1) at room temperature. (C) 2012 Elsevier B.V. All rights reserved.