Abstract: Two kinds of monodispersed SiO₂ TiO₂ composite particles with the uniform diameter of 18 nanometers and 40 nanometers separately were prepared by sol technology,and the best synthesis condition was also determined. Electron microscope revealed that the hydrated TiO 2 particle had been grafted onto the surface of SiO 2 particle, growing outside in a needle shape. Study on the covering process,the calcination behavior of the composite ultrafine powder and the surface modification displayed that the crystal form of TiO 2 transformed from anatase to rutile at 1100℃~1200℃, the o tridymite form of SiO 2 came into being in the same condition and the SiO₂ TiO₂ ultrafine powder modified by methanol could be redispersed well in ethanol.