To provide a method of efficiently and simply producing oxalyl fluoride by reaction of oxalyl chloride with an alkali metal fluoride in an aprotic solvent.

After or as a mixture of an alkali metal fluoride and an aprotic solvent is treated with ultrasonic waves, oxalyl chloride is allowed to react with the alkali metal fluoride to produce oxalyl fluoride. In this case, oxalyl fluoride can be simply produced in high yield by treating the reaction mixture with ultrasonic waves, even when the alkali metal fluoride has relatively large particle sizes.