Microcalorimetry, infrared spectroscopy, and reaction kinetics measurements were used to investigate the role of hydroxyl groups on sulfated zirconia in promoting n-butane isomerization at 423 K. The catalytic activity for a sample dried at 773 K is an order of magnitude lower compared to a sample dried at 588 K. However, the catalytic activity for the sample dried at 773 K is promoted by dosing approximately 75 mu mol/g of water onto the surface at 423 K. Larger doses of water poison the catalyst. Dehydration of the catalyst did not alter the heats of adsorption of n-butane, isobutane, or ammonia. Water dissociates upon adsorption on the sample dried at 773 K, producing new hydroxyl groups which increase the extinction coefficient for infrared absorbance of ammonium ions. It is proposed that these hydroxyl groups may aid n-butane isomerization by stabilizing species on the surface and/or by suppressing the irreversible reduction of surface sulfur species.