The present disclosure relates to a method of manufacturing a cathode composite for an all-solid-state battery and a method of manufacturing an all-solid-state battery including the same. In particular, the present disclosure relates to a method of manufacturing a cathode composite for an all-solid-state battery in which the cathode composite is manufactured by mixing a solid electrolyte, a conductive material and a cathode active material with a solvent, and then performing two-step vacuum drying, whereby interfacial resistance between the cathode active material, the solid electrolyte and the conductive material is reduced to thus increase ionic conductivity, thereby improving battery performance and capacity, and a method of manufacturing an all-solid-state battery including the same.