A method for manufacturing a positive active material for an all-solid Lithium-Sulfur battery includes preparing a lithium sulfide solution by dissolving lithium sulfide in anhydrous ethanol. A mixture is prepared by mixing a carbon fiber to the lithium sulfide solution. A lithium sulfide-carbon fiber composite is prepared by drying the mixture of the carbon fiber and the lithium sulfide solution to deposit the lithium sulfide on a surface of the carbon fiber. The lithium sulfide-carbon fiber composite is heated at 400 to 600° C.