The dehydration and rehydration of a catalytically active (superacid) sulfate-doped ZrO2 system has been studied by IR spectroscopy. By the adsorption of pyridine, the acidity of the system has been tested in various stages of the dehydration/rehydration process. Bronsted acid centers are abundantly present and are in different hydration states after dehydration at temperatures in the 300-473 K interval. For dehydration at T greater than or equal to 473 (but not higher than approximate to 900 K), declining amounts of acid protonic centers are still present and are in an anhydrous form; the original Bronsted acidity can be regenerated upon rehydration at ambient temperature.