The structure and electrical conductivity of the fast oxide ion conducting system BIZNVOX, Bi2ZnxV1-xO5.5-3x/2 (0.05 less than or equal to x less than or equal to 0.27), were investigated using X-ray powder diffraction and ac impedance spectroscopy. There is a compositional dependence of the conductivity behaviour as a function of temperature. This behaviour was correlated with the stabilisation of various polymorphs within the system. The x = 0.10 composition was found to have one of the highest low temperature conductivities (sigma(300) = 4.09 x 10(-3) S cm(-1)) for any BIMEVOX compound.