The present invention provides a sulfur-based positive electrode active material for use in a solid-state battery, comprising: 30-80 wt % of Li2S, 10-40 wt % of one or more second lithium compounds selected from LiI, LiBr, LiNO3, and LiNO2, and 0-30 wt % of a conductive carbon material; a method for preparing the sulfur-based positive electrode active material, a positive electrode including the sulfur-based positive electrode active material, and a solid-state battery including the positive electrode. The sulfur-based positive electrode active material and the positive electrode provide a high specific capacity and an increased discharge voltage.