Utilizing the raw materials of TiOSO4, NaOH, NH4NO3 and RDX, the TiO2 ultrafine particles were prepared under high pressure and high temperature by detonation method. The structure, composition and size distribution of the TiO2 ultrafine particles were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated the as-prepared TiO2 ultrafine particles exhibited spherical-like grains and that the average size of particles was 25.5nm. After being heated at 700 8C for 1 h, TiO2 particles have entirely completed the anatase-rutile phase transition, which means that detonation method can effectively enhance the anatase-rutile phase transition by lowering the transition temperature. The size of TiO2 nanoparticles can be effectively controlled because the as-prepared nanoparticles do not have enough time to grow to large and perfect crystallites during the detonation process.