A new lithium ion conductor, thio-LISICON (Lithium SuperIonic CONductor), Li2ZrS3 was synthesized by solid state reaction. It has the lithium ion conductivity of 7.3 x 10(-6) S cm(-1) at 30 degrees C. Its conductivity were successfully improved by introducing interstitial lithium ions with Zr4+ partially substituted by Zn2+ (Li2+2xZnxZr1-xS3; x=0, 0.05, 0.1, 0.2, 0.4). The optimum x value for introducing the highest content of interstitial lithium ions was found to be 0.1. And the highest ionic conductivity at 30 degrees C was reached to be 1.2 x 10(-4) S cm(-1). (c) 2008 Elsevier B.V. All rights reserved.