In the study, strontium titanium (SrTiO3) nanoparticles were successfully synthesized by a single-step direct hydrothermal process under alkaline condition from crystalline P25 titanium dioxide (TiO2) powders and strontium hydroxide octahydrate (Sr(OH)(2)center dot 8H(2)O) at 220A degrees C. The samples obtained were characterized by X-ray diffraction (XRD), indicating that the products were highly crystalline cubic SrTiO3 nanoparticles. The lattice parameter, unit cell volume, and atomic position were refined by Highscore Plus and Maud program to determine the crystal structure parameters. The thermal field emission scanning electron microscope and energy-dispersive spectrometer (FE-SEM-EDS) showed the samples prepared were cubic SrTiO3 nanoparticles with regular morphology. The fine morphologies and structures of SrTiO3 were investigated by field emission high-resolution transmission electron microscope (HR-TEM). The specific surface areas of samples were investigated by the BET method. As a comparison, SrTiO3 nanoparticles also were synthesized by solid-state reaction. The samples synthesized by hydrothermal method have bigger specific surface areas and smaller grain sizes than the sample synthesized by solid-state method. Big mole ratio Sr/Ti and short reaction time are helpful to produce small particles with large specific surface area. The reaction mechanism of the hydrothermal process was illustrated finally.