To provide a method for producing a 1,2,4-thiadiazine-1,1-dioxide compound from a readily available raw material in a short process in good yield.

The method for producing the 1,2,4-thiadiazine-1,1-dioxide compound represented by general formula (I) is carried out by subjecting a 2-acylaminobenzenesulfonamide compound represented by general formula (II) to a cyclization reaction in the presence of a tetrahalomethane and triphenylphosphine in an organic solvent (in general formulas (I) and II, R1 denotes a substituted or an unsubstituted alkyl group or aryl group; R2s denote each a substituent; n denotes an integer of ≥0 and ≤4; the plurality of R2s may be each the same or different when n is ≥2 and may mutually be bound to form a ring; R3 denotes a substituent).