The effects of transition metal promoters on the thermal stability of sulfated zirconia (SZ) were studied by XRD and Raman spectroscopy. After calcination at 750 degreesC, the proportion of the monoclinic phase in SZ and 2.7 wt% Fe-SZ were 58 and 13%, respectively. Ni showed a smaller effect and Co showed a negative effect for the stabilization of the tetragonal phase. The results were compared with those of nonsulfated Fe-loaded zirconia, and it was suggested that Fe forms a solid solution with sulfated zirconia.