The structure and electric conductivity of the fast oxide ion conductors Bi-13(Mo,M)(5)O-34, i.e. Bi[Bi12O14][(MO,M)O-4](5) With M = Li, Mg, Al, Si, Ge and V were investigated using X-ray powder diffraction experiments and AC impedance spectroscopy. The compounds of this original family are isostructural with Bi13Mo4VO34; they crystallize in the monoclinic system with the space group P2/c. The structures exhibit typical [Bi12O14](n) columns developed along [010], surrounded by (Mo,M)O-4 tetrahedra packed in layers parallel to (100) and (001), the electrical balance of the network being achieved by Bi atoms at the intersection of these planes. The syntheses, X-ray powder pattern analyses and conductivity measurements are reported; the best anionic conductor of the family is proved to be Bi[Bi12O14][(Mo0.933Al0.067)O-4](5) with sigma(980) (K) = 1.4 x 10 (-2) S cm(- 1).