Sulfated binary and trinary oxide solid superacids were prepared and characterized. The incorporation of Cr, Fe, Mn and V into sulfated zirconia increases its superacidity and catalytic activity for n-butane isomerization at 35 degrees C significantly. The catalytic activity of sulfated oxides of Cr-Zr, Fe-Cr-Zr and Fe-V-Zr is 2-3 times greater than that of the well-known sulfated Fe-Mn-Zr oxide. A negative effect was observed in the cases of sulfated Mn-Zr, Sn-Zr, W-Zr and Mo-Zr oxides. The origin of the enhancement in superacidity and activity is discussed in the light of experimental results obtained by XRD, IR and chemical analysis.