Surface characterization of a sulfate-derived zirconia sample containing approximately 1 wt% S was performed by IR spectroscopy. Several types of sulfate groups were detected which are resistant to heating in vacuo up to 973 K. By using CO as a spectroscopic probe, two kinds of Lewis acid sites were identified which were assigned to surface Zr4+ ions in different environments. Comparison with corresponding data for a nearly sulfate-free zirconia sample showed that sulfated zirconia has an enhanced Lewis acidity.