A composition for forming an active material layer, including a sulfide-based solid electrolyte, an active material, a conductive auxiliary agent including a carbonaceous material, and a dispersion medium, in which the dispersion medium includes at least one ketone compound dispersion medium in which two aliphatic groups each having 4 or more carbon atoms are bonded to a carbonyl group; a method for manufacturing the composition for forming an active material layer; a method for manufacturing a solid electrolyte-containing sheet; and a method for manufacturing an all-solid state secondary battery.