We recently described a new family of oxide anion conductors with a structure based on [Bi 12 O 14 ] ∞ columns (J. Solid. State Chem.122, 394 (1996)). The parent compound of this series can be formulated as Bi 26 Mo 10 O 69 and formation of a solid solution, in the Bi 2 O 3 –MoO 3 binary system, in the range 2.57≤Bi/Mo≤2.77 was established. The stoichiometry of this series was questioned by R. Enjalbertet al.(J. Solid State Chem.131, 236 (1997)), but confirmed by D. J. Buttreyet al.(Mater. Res. Bull.32, 947 (1997)). The first part of this paper is devoted to a refutation criticisms by R. Enjalbertet al.In the second part, a comparison with other Bi 2 O 3 -based oxide anion conductors enables us to propose an iono-covalent description of this novel structure type, taking into account all the structural and electrical features, especially new neutron powder diffraction refinement and conductivity measurements under variable oxygen partial pressures.