Bismuth-aluminum binary-oxide layers and clusters on an Al2O3 surface were prepared by supporting bismuth triethoxides on Al2O3, followed by calcination at 673 K. The Bi-Al binary oxides were characterized by EXAFS and XPS, and their catalytic activities for ethanol-selective oxidation were investigated. XPS data revealed that Bi atoms were supported on the Al2O3 surface in a Stranski-Krastanov (SK) growth mode, while EXAFS data demonstrated that Bi atoms made bondings with Al atoms at 0.353-0.361 nm through oxygen atoms (Bi-O, 0.211-0.212 nm) irrespective of Bi loadings and that the coordination numbers (CN) of the Bi-Al bond did not significantly change with Bi loadings (CN, 1.0-1.5). It is likely from these results that below 9 wt % Bi loading, Bi-Al (rich) binary-oxide monolayers are formed at the Al2O3 surface and that above 9 wt % Bi loading, Bi (rich)-Al binary-oxide clusters grow on the surface. In the low-Bi-loading catalysts, Bi-O and Bi-Al bonds were observed at 0.211 and 0.353-0.355 nm, respectively, while no Bi-Bi bond was observed, which suggests that Bi atoms are dispersed in the oxide layers. On the other hand, in the high-Bi-loading catalysts, Bi-Bi and long Bi-O bonds were observed at 0.363-0.369 and 0.276-0.279 nm, respectively, in addition to Bi-O at 0.212 nm and Bi-Al at 0.359-0.361 nm. The distances of the long Bi-O and Bi-Bi bonds were comparable to their distances in gamma -Bi2O3, and the BI-AI distance was also close to that in bismuth binary oxides with the gamma -Bi2O3 phase. These results suggest that the Bi (rich)-Al binary-oxide clusters have a gamma -Bi2O3-like structure. The catalytic activity of these binary oxides at the Al2O3 surface for ethanol-selective oxidation strongly depended on the structure around bismuth atoms. The initial rate for acetaldehyde formation steeply increased around 9 wt % Bi loading. The activation energy for the 11.0 wt % Bi/Al2O3 catalyst was 53 kJ mol(-1), while that for the 7.6 wt % Bi/Al2O3 catalyst was 96 kJ mol(-1), reflecting the different local structure of the active Bi sites.