A series of Al2O3-SnO2 Catalysts with the mole ratio of Al2O3 to SnO2 equal to 1 : 1, 1 : 0.5,1 : 0.1,1 : 0.05 and 1 : 0.01 were characterized by P-31 NMR of adsorbed trimethyl phosphine (TMP) and Sn-119 MAS NMR spectroscopy. It was found from P-31 NMR that no Bronsted acid sites exist in these samples. Pure SnO2 shows two different types of Lewis acid sites; in the mixed oxide samples a Lewis peak characteristic of pure Al2O3 is always seen, together with either one or two other Lewis peaks, depending on the Sn concentration. Sn-119 CP/MAS NMR spectra of the highest Sn-content sample show one narrow line at -603 ppm superimposed on a very broad line, indicating a strong interaction between Al and Sn oxides.