Pseudobrookite (Fe2TiO5) was prepared from Fe2O3-TiO2 mixtures at 850 and 950 degrees C in air, argon and chlorine atmospheres. In the latter case, an experimental arrangement in which Fe2O3 and TiO2 were placed in separated compartments under the same chlorine atmosphere was also used. Pseudobrookite was identified by X-ray powder diffraction and microstructurally characterized by scanning electron microscopy. The very different pseudobrookite morphologies in each atmosphere allow us to propose that the formation mechanism involves Ti4+ diffusion in the Fe2O3 surface in air and argon atmospheres and vapour transport through FeCl3(g) and TiCl4(g) in the chlorine atmosphere.