A method of treating the surface of a positive electrode active material that is capable of inhibiting a reaction at the interface between a sulfide-based solid electrolyte and the positive electrode active material. A positive electrode active material particle for sulfide-based all-solid-state batteries, the surface of which is reformed, using the method and a sulfide-based all-solid-state battery, the charge/discharge characteristics of which are improved, including the same are also disclosed. The positive electrode active material particle for sulfide-based all-solid-state batteries manufactured using a dry-type method exhibits larger capacity than a positive electrode active material particle for sulfide-based all-solid-state batteries manufactured through a conventional wet-type process. In addition, the manufacturing process is simplified, and the amount of byproducts is reduced.