Hydrous TiO₂ powders were obtained from the TiCl₄ precursor precipitated under different pH values by adding aqueous ammonia. The prepared titania exists in the form of nanocrystalline anatase with some brookite phase. The volume fraction of brookite phase increases with the decrease of the synthesized pH value. The beginning and ending temperature for anatase–rutile transition increases with the increase of synthesized pH value. Several parameters corresponding to the phase transformation of nanocrystalline titania, such as particle size, surface area and the polytype phase, have been discussed. The presence of brookite phase in the powders is responsible for enhancing the anatase–rutile transformation.