To provide a method of producing a langasite-type oxide single crystal wafer, by which the formation of undulation of the surface of the wafer or of a local deep unevenness on the surface of the wafer can be suppressed and the langasite-type oxide single crystal wafer almost free from warps can be easily obtained without generating harmful gas such as NOx.

The method of producing the langasite-type oxide single crystal wafer includes a process for cutting out a wafer 10 having a prescribed thickness by slicing an ingot 1B, a process for grinding both surfaces of the wafer 10, a process for polishing the surface of the both surface-ground wafer 10A to make it a mirror surface, and a process for heat treating the wafer 10C having the mirror surface at a temperature of ≤1,000°C or a process for heat treating the wafer 10A whose both surfaces have been ground at a temperature of ≤1,000°C and polishing the surface of the wafer 10D subjected to heat treatment to make it mirror surface.