The invention is to provide a novel method for producing a solid electrolyte having a high ionic conductivity according to a liquid-phase method. The production method for a solid electrolyte includes mixing a raw material inclusion containing a lithium atom, a sulfur atom, a phosphorus atom and a halogen atom with a complexing agent and a solvent, wherein the amount of the complexing agent is 0.1 mL or more and 4.0 mL or less relative to 1 g of the total mass of the raw material inclusion.