The catalytic behavior of SO42--ZrO2 in the n-butane isomerization reaction was studied. Both ZrO2 crystalline structure and SO42- concentration were analyzed. ZrO2 samples were obtained from ZrCl4 in different reaction media, thus allowing us to obtain tetragonal and monoclinic phases separately. The SO42- concentration over ZrO2 was the same by sulfating amorphous or crystalline materials. The sulfate addition over amorphous Zr(OH)(4) generated strong acid sites, which are active in n-butane isomerization. The catalytic activity showed a maximum at calcination temperatures between 873 and 893 K, where the Lewis acidity is higher. The tetragonal phase is present under these conditions, as shown by XRD patterns. The same results were obtained with samples synthesized from another precursor. Coke deposition or water presence produced catalyst deactivation.