The present invention provides a method for producing a 1,2-benzisothiazol-3-one compound whereby the alkyl halide by-product that is generated when a 2-(alkylthio)benzonitrile compound and a halogenation agent are reacted in the presence of water is reacted with a sulfide to become an alkylthiol and then, as an alkali metal salt, is reacted with a 2-halobenzonitrile compound in order to be converted to a 2-(alkylthio)benzonitrile compound and reused as a starting material for the production of a 1,2-benzisothiazol-3-one compound. By means of the present invention, it is possible to efficiently use the by-product that is generated during the production of a 1,2-benzisothiazol-3-one compound and economically produce a 1,2-benzisothiazol-3-one compound without placing a burden on the environment.
