PURPOSE: To easily obtain a substituted benzoyl chloride derivative useful as an intermediate for agrochemicals, medicines, etc., (e.g. herbicides), by chlorinating a substituted benzoic acid derivative.

CONSTITUTION: This derivative of formula I (Y is a halogen; R4 is a lower alkyl)(pref. 5-acetylthio-4-chloro-2-fluorobenzoyl chloride) is obtained by chlorinating (A) a substituted benzoic acid derivative of formula II (e.g. 5-acetylthio-2,4- difluorobenzoic acid) with (B) pref. thionyl chloride at the equivalent ratio B/A of pref. (1 10). The reaction is pref. conducted in the absence of any solvent or in a solvent such as dichloromethane at 20-150°C, etc.