Acid-base properties of alumina-supported rare-earth oxides (Ln/Al2O3; Ln = La, Ce, Eu, Tb, and Yb) were investigated with alpha -pinene isomerization, 2-butanol decomposition, and temperature-programmed desorption and FTIR techniques. The structural characterization was carried out by means of XRD, Raman, and XAFS spectroscopies. Differences in the catalyses, acid-base properties, and structures of Ln/Al2O3 catalysts because of loaded elements and the amounts were discussed. The addition of a lanthanoid atom (Ln) to gamma -Al2O3 poisons both the original base and acid sites of gamma -Al2O3 and generates new-type Lewis acid site. In a series of Ln/Al2O3 catalysts, 0.2-0.5 mmol of Yb/Al2O3 exhibited the highest activity for alpha -pinene isomerization. The supported Yb species form Yb-O-Al linkage which acts as a Lewis acid. The local structure around Yb and a generation mechanism of acidic property are analogous with Yb/Al2O3 and Yb/SiO2.