The n-butane isomerization activity of a mesoporous sulfated zirconia is shown to he a strong function of the extent of hydration on the catalyst surface. Regeneration of the catalyst at 500 degreesC in oxygen must be followed by a water exposure step to rehydrate the catalyst and recapture its original activity. Pretreatment drying procedures are critical in determining optimal activity on the mesoporous catalyst. Pretreating at 400 degreesC leads to the most active mesoporous sulfated zirconia catalyst for n-butane isomerization.