The influence of high Mg2+ dopant levels in BIMGVOX, Bi2MgxV1-xO5.5-3x/2 (0.05 less than or equal tox less than or equal to0.40) on structure and conductivity has been investigated using X-ray powder diffraction and a.c. impedance spectroscopy. Four, compositionally dependent. structural ranges are observed at room temperature, with emergence of a new orthorhombic phase at high dopant levels. Generally the Arrhenius plots of conductivity show two linear regions the limits of which an compositionally dependent. The results have been correlated to the stability ranges of various polymorphs within the system.