Disclosed is a means for producing a highly pure 2-hydroxy-4-oxa-5-thiatricyclo[4.2.1.03,7]nonane 5,5-dioxide derivative from a highly pure and industrially available starting material industrially and in high yield. Specifically disclosed is a process for producing a sultone derivative. The process comprises the following steps (A) and (B): (A) hydrolyzing a sulfonylhalide derivative represented by chemical formula (1) or an enantiomer thereof to yield a sulfonic acid derivative; and (B) treating the sulfonic acid derivative with an oxidizing agent to yield a corresponding sultone derivative represented by chemical formula (2) or an enantiomer thereof.
