The synthesis of 3,4-dihydro-1H-2,3-benzothiazine 2,2-dioxides and 1,2,4,5-tetrahydro-3,2-benzothiazepine 3,3-dioxides is studied using sulfated zirconia as catalyst. The sulfated zirconia calcined at 550 A degrees C achieved a high selectivity which is attributed to the formation of a tetragonal phase. In addition, the catalyst can be reused up to three times without loss of its catalytic activity.