The phase reactions of V-doped clays in brick burning processes are studied to evaluate the utilization of V-containing wastes in brickworks. V2O5 was admixed to clay and annealed at temperatures between 200 and 1000 °C. The formation of mullite, cristobalite, and a pseudobrookite compound is observed between 700 and 800 °C. These phases do not occur in pure clay annealed in the corresponding temperature range. The samples were investigated with X-ray powder diffraction methods, quantitative analyses were performed with the Rietveld method and chemical analyses with X-ray fluorescence spectroscopy. Analytical Transmission Electron Microscopy showed incorporation of vanadium and iron in mullite.