Provided is an anode active material configured to achieve both an increase in the coulombic efficiency during initial charge and discharge of an all-solid-state battery, and suppression of an increase in the resistance of the all-solid-state battery. The anode active material may be an anode active material, wherein the anode active material is an anode active material for use in all-solid-state batteries; wherein the anode active material comprises a lithium-silicon alloy and elemental silicon; and wherein the anode active material has peaks at positions of 2θ=20.2°±0.5°, 23.3°±0.5°, 40.5°±0.5°, and 46.0°±0.5° in a XRD spectrum obtained by XRD measurement using CuKα radiation.