The new BIMEVOX series Bi(4)V(2-x)M(x)O(11) (M = Sb, Nb) have been investigated by X-ray powder diffraction, thermal analysis and ionic conductivity measurements. Structural phase transitions alpha<->beta and beta<->gamma occur as a function of composition. The structure of the tetragonal phases Bi4V1.5Sb0.5O11, Bi4VSbO11 and Bi4V1.5Nb0.5O11 have been refined by the Rietveld method. Structure and conductivity are compared in function of the substitution fate of vanadium. The gamma-type Bi4V1.7Sb0.3O11 phase exhibits the best O2--anionic conductivity at low temperature : 10(-2)S.cm(-1) at 590 K, associated with a low activation energy E(a)= 0.6 eV.