Supported sulfated zirconia catalysts with zirconia contents of 10, 20 and 50 wt% were prepared by impregnation of SiO2 and gamma-Al2O3 supports with H2SO4/ Zr(SO4)(2) solutions followed by calcination at 923 K. The catalysts were characterized by X-ray diffraction, extended X-ray absorption fine structure measurements, thermal analysis, UV-vis spectroscopy, and electron microscopy. Tetragonal zirconia was detected in all silica-supported samples but only in the 50 wt% zirconia-containing alumina-supported sample, indicating high dispersion of zirconia on alumina. Alumina-supported samples retained additional sulfate, at least in part as Al-2(SO4)(3). All samples were active in n-butane isomerization (1 kPa n-butane, 378 K). There was no relation between the presence of tetragonal zirconia in these samples and the catalytic performance.