The unit cells of alpha-Bi2Mo3O12, beta-Bi2Mo2O9, and gamma(H)-Bi2MoO6 are visualized by the crystal structure application. These oxides have twin Mo tetrahedra structures. The visualization clarified that Mo ions of twin Mo tetrahedra and some Bi ions with these Bi-Mo oxides lie on the same plane. It is proposed that the active sites for selective oxidation is linked with these structures exposed on the surface. (C) 2004 Elsevier B.V. All rights reserved.