Hydrogen assisted magnesiothermic reduction (HAMR) of TiO2 is a promising new process developed recently to produce Ti metal with low cost and less energy consumption. This work focuses on the understanding and optimization of the reduction process to control the quality of the reduced product. TiO2 precursor particles with different relative densities were prepared, and the effects of the relative densities on reduction by Mg in H-2 were studied. The changes of oxygen contents vs. reduction time at various temperatures were investigated. The phase transformations during the reduction were analyzed both theoretically and experimentally. The relationship between the morphology of the reduced products and the relative densities of the TiO2 precursors was analyzed by SEM characterization and the likely reason for the morphology evolution was discussed. (C) 2018 Elsevier Ltd. All rights reserved.